Pilot trial of intravenous infusion of a replication-selective adenovirus (ONYX-015) in combination with chemotherapy or IL-2 treatment in refractory cancer patients

Oncolytic virotherapy in lung cancer

Lung tumors are one of the most aggressive threats affecting humans. Current therapeutic approaches have improved patients' survival; however, further efforts are required to increase effectiveness and protection against tumor relapse and metastasis. Immunotherapy presents an alternative to previous treatments that focuses on stimulating of the patient's immune system to destroy tumor cells. Viruses can be used as part of the immune therapeutic approach as agents that could selectively infect tumor cells, triggering an immune response against the infection and against the tumor cells. Some viruses have been selected for specifically infecting and destroying cancer cells, activating the immune response, enhancing access, amplifying the cytotoxicity against the tumor cells, and improving the long-term memory that can prevent tumor relapse. Oncolytic virotherapy can then be used as a strategy to target the destruction of transformed cells at the tumor site and act in locations distant from the primary targeted tumor site. Some of the current challenges in lung cancer treatment can be addressed using traditional therapies combined with oncolytic virotherapy. Defining the best combination, including the choice of the right settings will be at the next frontier in lung cancer treatment.

The impact of oncolytic adenoviral therapy on the therapeutic efficacy of PD-1/PD-L1 blockade

Immunotherapy has revolutionized treatment of cancer during the last decades. Oncolytic virotherapy has also emerged as a strategy to fight against cancer cells both via lysis of malignant cells and activating immune responses. Accepted as a logical strategy, combination of monoclonal antibodies particularly against the programmed death-1 (PD-1) and programmed death-ligand 1 (PD-L1) is introduced to improve clinical responses to immune checkpoint inhibitors (ICIs). Accordingly, Talimogene laherparepvec (T-VEC) has received approval for clinical use, while a number of oncolytic Adenoviruses (Ads) are being investigated in clinical trials of malignancies. Combination of oncolytic Ads with PD-1/PD-L1 inhibitors have shown potentials in promoting responses to ICIs, changing the tumor microenvironment, inducing long-term protection against tumor, and promoting survival among mice models of malignancies. Regarding the increasing importance of oncolytic Ads in combination therapy of cancers, in this review we decide to outline recent studies in this field.

Oncolytic viruses: challenges and considerations in an evolving clinical landscape

Despite advances in treatment, cancer remains a leading cause of death worldwide. Although treatment strategies are continually progressing, cancers have evolved many mechanisms for evading therapies and the host immune system. Oncolytic viruses (OVs) could provide a much-needed option for cancers that are resistant to existing treatments. OVs can be engineered to specifically target and kill cancer cells, while simultaneously triggering an immune response at the site of infection. This review will focus on the challenges of developing a successful OV and translation to clinical practice, discussing the innovative strategies that are being used to optimize the potential of OVs. Here, we will also explore the current clinical landscape and the prospects of OVs in early clinical development.

The Evolution and Future of Targeted Cancer Therapy: From Nanoparticles, Oncolytic Viruses, and Oncolytic Bacteria to the Treatment of Solid Tumors

While many classes of chemotherapeutic agents exist to treat solid tumors, few can generate a lasting response without substantial off-target toxicity despite significant scientific advancements and investments. In this review, the paths of development for nanoparticles, oncolytic viruses, and oncolytic bacteria over the last 20 years of research towards clinical translation and acceptance as novel cancer therapeutics are compared. Novel nanoparticle, oncolytic virus, and oncolytic bacteria therapies all start with a common goal of accomplishing therapeutic drug activity or delivery to a specific site while avoiding off-target effects, with overlapping methodology between all three modalities. Indeed, the degree of overlap is substantial enough that breakthroughs in one therapeutic could have considerable implications on the progression of the other two. Each oncotherapeutic modality has accomplished clinical translation, successfully overcoming the potential pitfalls promising therapeutics face. However, once studies enter clinical trials, the data all but disappears, leaving pre-clinical researchers largely in the dark. Overall, the creativity, flexibility, and innovation of these modalities for solid tumor treatments are greatly encouraging, and usher in a new age of pharmaceutical development.

Development of oncolytic viruses for cancer therapy

Oncolytic virotherapy is a therapeutic approach that uses replication-competent viruses to kill cancers. The ability of oncolytic viruses to selectively replicate in cancer cells leads to direct cell lysis and induction of anticancer immune response. Like other anticancer therapies, oncolytic virotherapy has several limitations such as viral delivery to the target, penetration into the tumor mass, and antiviral immune responses. This review provides an insight into the different characteristics of oncolytic viruses (natural and genetically modified) that contribute to effective applications of oncolytic virotherapy in preclinical and clinical trials, and strategies to overcome the limitations. The potential of oncolytic virotherapy combining with other conventional treatments or cancer immunotherapies involving immune checkpoint inhibitors and CAR-T therapy could form part of future multimodality treatment strategies.

Virus-Receptor Interactions and Virus Neutralization: Insights for Oncolytic Virus Development

Oncolytic viruses (OVs) are replication competent agents that selectively target cancer cells. After penetrating the tumor cell, viruses replicate and eventually trigger cell lysis, releasing the new viral progeny, which at their turn will attack and kill neighbouring cells. The ability of OVs to self-amplify within the tumor while sparing normal cells can provide several advantages including the capacity to encode and locally produce therapeutic protein payloads, and to prime the host immune system. OVs targeting of cancer cells is mediated by host factors that are differentially expressed between normal tissue and tumors, including viral receptors and internalization factors. In this review article, we will discuss the evolution of oncolytic viruses that have reached the stage of clinical trials, their mechanisms of oncolysis, cellular receptors, strategies for targeting cancers, viral neutralization and developments to bypass virus neutralization.

Gene Therapy in Head and Neck Cancer

Although overall cancer death rates are decreasing, comparative improvements in head and neck squamous cell cancer are modest. Although new advances targeting immune checkpoints may soon improve these numbers, additional research for new therapeutic options is vital. One potential treatment avenue is the use of gene therapy. This article provides insight into some gene therapy targets and varied techniques being evaluated for patients with head and neck cancer. Techniques include corrective gene therapy, cytoreductive gene therapy, and gene editing, in addition to a discussion on gene therapy vectors.

Oncolytic immunotherapy: unlocking the potential of viruses to help target cancer

Oncolytic immunotherapy is a research area of cancer immunotherapy investigating the use of modified viruses to target cancer cells. A variety of different viral backbones (e.g., adenovirus, reovirus) with a diverse range of genetic modifications are currently being investigated for the treatment of a variety of cancers. The oncolytic virus that has advanced the furthest in clinical development is talimogene laherparepvec, a recombinant HSV-1 virus expressing granulocyte-macrophage colony-stimulating factor (GM-CSF). In a phase 3 study in patients with unresectable metastatic melanoma, intralesional talimogene laherparepvec treatment resulted in a higher durable response rate compared with subcutaneous GM-CSF treatment (16.3 versus 2.1%; P < 0.001). Notably, responses were observed at uninjected lesions including visceral lesions, indicating a systemic antitumor response had occurred. Studies evaluating combination treatments involving oncolytic viruses and immunologic agents are ongoing. This review focuses on the mechanisms of action for oncolytic viruses and highlights select agents and combinations currently in development.

Immune System, Friend or Foe of Oncolytic Virotherapy?

Oncolytic viruses (OVs) are an emerging class of targeted anticancer therapies designed to selectively infect, replicate in, and lyse malignant cells without causing harm to normal, healthy tissues. In addition to direct oncolytic activity, OVs have shown dual promise as immunotherapeutic agents. The presence of viral infection and subsequently generated immunogenic tumor cell death trigger innate and adaptive immune responses that mediate further tumor destruction. However, antiviral immune responses can intrinsically limit OV infection, spread, and overall therapeutic efficacy. Host immune system can act both as a barrier as well as a facilitator and sometimes both at the same time based on the phase of viral infection. Thus, manipulating the host immune system to minimize antiviral responses and viral clearance while still promoting immune-mediated tumor destruction remains a key challenge facing oncolytic virotherapy. Recent clinical trials have established the safety, tolerability, and efficacy of virotherapies in the treatment of a variety of malignancies. Most notably, talimogene laherparepvec (T-VEC), a genetically engineered oncolytic herpesvirus-expressing granulocyte macrophage colony stimulating factor, was recently approved for the treatment of melanoma, representing the first OV to be approved by the FDA as an anticancer therapy in the US. This review discusses OVs and their antitumor properties, their complex interactions with the immune system, synergy between virotherapy and existing cancer treatments, and emerging strategies to augment the efficacy of OVs as anticancer therapies.

The Use of Gene Therapy in Cancer Research and Treatment

Gene therapy involves identifying a gene of interest and then manipulating the expression of this gene through a variety of techniques. Here we specifically address gene therapy's role in cancer research. This paper will encompass thoroughly investigated techniques such as cancer vaccines and suicide gene therapy and the latest advancements in and applications of these techniques. It will also cover newer techniques such as Antisense Oligonucleotides and small interfering RNAs and how these technologies are being developed and used. The use of gene therapy continues to expand in cancer research and has an integral role in the advancement of cancer treatment.

Oncolytic viruses in head and neck cancer: a new ray of hope in the management protocol

This paper intends to highlight the different types of oncolytic viruses (OVs), mechanism of tumor specificity, its safety, and various obstacles in the design of treatment and combination therapy utilizing oncotherapy. Search was conducted using the internet-based search engines and scholarly bibliographic databases with key words such as OVs, head and neck cancer, viruses, oral squamous cell carcinoma, and gene therapy. Revolutionary technologies in the field of cancer treatment have gone through a series changes leading to the development of innovative therapeutic strategies. Oncolytic virotherapy is one such therapeutic approach that has awaited phase III clinical trial validation. OVs are self-replicating, tumor selective and lyse cancer cells following viral infection. By modifying the viral genome, it is possible to direct their toxicity toward cancer cells. Viruses that are used for treatment of head and neck cancer are either naturally occurring or genetically modified. OVs are tumor selective and potential anticancer agents. Virotherapy may become the standard of care and part of combination therapy in the management of head and neck cancer in the future.

Encapsulation of adenovirus serotype 5 in anionic lecithin liposomes using a bead-based immunoprecipitation technique enhances transfection efficiency

Oncolytic viruses (OVs) constitute a promising class of cancer therapeutics which exploit validated genetic pathways known to be deregulated in many cancers. To overcome an immune response and to enhance its potential use to treat primary and metastatic tumors, a method for liposomal encapsulation of adenovirus has been developed. The encapsulation of adenovirus in non-toxic anionic lecithin-cholesterol-PEG liposomes ranging from 140 to 180 nm in diameter have been prepared by self-assembly around the viral capsid. The encapsulated viruses retain their ability to infect cancer cells. Furthermore, an immunoprecipitation (IP) technique has shown to be a fast and effective method to extract non-encapsulated viruses and homogenize the liposomes remaining in solution. 78% of adenovirus plaque forming units were encapsulated and retained infectivity after IP processing. Additionally, encapsulated viruses have shown enhanced transfection efficiency up to 4 × higher compared to non-encapsulated Ads. Extracting non-encapsulated viruses from solution may prevent an adverse in vivo immune response and may enhance treatment for multiple administrations.

Chapter eight--Oncolytic adenoviruses for cancer immunotherapy: data from mice, hamsters, and humans

Adenovirus is one of the most commonly used vectors for gene therapy and two products have already been approved for treatment of cancer in China (Gendicine(R) and Oncorine(R)). An intriguing aspect of oncolytic adenoviruses is that by their very nature they potently stimulate multiple arms of the immune system. Thus, combined tumor killing via oncolysis and inherent immunostimulatory properties in fact make these viruses in situ tumor vaccines. When further engineered to express cytokines, chemokines, tumor-associated antigens, or other immunomodulatory elements, they have been shown in various preclinical models to induce antigen-specific effector and memory responses, resulting both in full therapeutic cures and even induction of life-long tumor immunity. Here, we review the state of the art of oncolytic adenovirus, in the context of their capability to stimulate innate and adaptive arms of the immune system and finally how we can modify these viruses to direct the immune response toward cancer.

Systemic therapy strategies for head-neck carcinomas: Current status

Head and neck cancers, most of which are squamous cell tumours, have an unsatisfactory prognosis despite intensive local treatment. This can be attributed, among other factors, to tumour recurrences inside or outside the treated area, and metastases at more distal locations. These tumours therefore require not only the standard surgical and radiation treatments, but also effective systemic modalities. The main option here is antineoplastic chemotherapy, which is firmly established in the palliative treatment of recurrent or metastatic stages of disease, and is used with curative intent in the form of combined simultaneous or adjuvant chemoradiotherapy in patients with inoperable or advanced tumour stages. Neoadjuvant treatment strategies for tumour reduction before surgery have yet to gain acceptance. Induction chemotherapy protocols before radiotherapy have to date been used in patients at high risk of distant metastases or as an aid for decision-making ("chemoselection") in those with extensive laryngeal cancers, prior to definitive chemoradiotherapy or laryngectomy. Triple-combination induction therapy (taxanes, cisplatin, 5-fluorouracil) shows high remission rates with significant toxicity and, in combination with (chemo-)radiotherapy, is currently being compared with simultaneous chemoradiotherapy; the current gold standard with regards to efficacy and long-term toxicity.A further systemic treatment strategy, called "targeted therapy", has been developed to help increase specificity and reduce toxicity. An example of targeted therapy, EGFR-specific antibodies, can be used in palliative settings and, in combination with radiotherapy, to treat advanced head and neck cancers. A series of other novel biologicals such as signal cascade inhibitors, genetic agents, or immunotherapies, are currently being evaluated in large-scale clinical studies, and could prove useful in patients with advanced, recurring or metastatic head and neck cancers. When developing a lasting, individualised systemic tumour therapy, the critical evaluation criteria are not only efficacy and acute toxicity but also (long-term) quality-of-life and the identification of dedicated predictive biomarkers.

Deletion analysis of Ad5 E1a transcriptional control region: impact on tumor-selective expression of E1a and E1b

The regulatory sequences upstream of E1a, the first viral protein expressed upon infection of cells with adenovirus, have binding sites for multiple transcription factors including two binding sites for E2f and five binding sites for Pea3. We evaluated the impact of deletions, which remove one or more of these transcription factor-binding sites on the expression of E1a in a panel of tumor cells and non-transformed cells. We demonstrated that specific deletions in the E1a enhancer markedly reduced the expression of E1a in growth-arrested cells while having a minimal impact on the expression of E1a in a panel of tumor cells. In particular, deletion of a 50-bp region located from -305 to -255 upstream of the E1a initiation site resulted in marked reduction of E1a and E1b expression and cytolytic activity in growth-arrested cells, while retaining near wild-type of expression of E1a and E1b and cytolytic activity in tumor cells. This deletion removed two Pea3 sites and one E2f site. The characteristics of this vector, TAV-255, was compared with dl1520 (Onyx-015) and demonstrated restricted cytolytic activity in growth-arrested cells similar to dl1520 and superior cytolytic activity in a panel of tumor cell lines. In this current study, we demonstrate that TAV-255, an E1a enhancer deletion vector, possesses tumor selective expression of both E1a and E1b along with potent tumor-selective oncolytic activity.

Clinical development directions in oncolytic viral therapy

Oncolytic virotherapy is an emerging experimental treatment platform for cancer therapy. Oncolytic viruses are replicative-competent viruses that are engineered to replicate selectively in cancer cells with specified oncogenic phenotypes. Multiple DNA and RNA viruses have been clinically tested in a variety of tumors. This review will provide a brief description of these novel anticancer biologics and will summarize the results of clinical investigation. To date oncolytic virotherapy has shown to be safe, and has generated clinical responses in tumors that are resistant to chemotherapy or radiotherapy. The major challenge for researchers is to maximize the efficacy of these viral therapeutics, and to establish stable systemic delivery mechanisms.

Current status of experimental therapeutics for head and neck cancer

As with many cancers, early detection of head and neck cancer increases a patient's survival rate. If diagnosed early, its five-year survival nears 90% with standard therapy alone. Unfortunately, the average survival rate for head and neck cancer is low due to the difficulty in early detection and achieving a sustainable response. Conventional treatments are not adequate for the majority of advanced or recurrent head and neck cancer patients because of the remarkable resistance of tumors to chemotherapy and radiation, and the situation is especially devastating for the first time treatment failure. The major limitations of these treatments are the lack of specificity for the tumor cell and unacceptable toxicity to the patient. As a result, current research in therapeutics for advanced, chemotherapy-resistant or recurrent head and neck cancer patients has focused on new treatment modalities that exploit biological differences between tumor and normal cells. These therapies include monoclonal antibodies, molecular inhibitors, gene therapy and photodynamic therapy. This article reviews the current preclinical and clinical evidence of these experimental therapeutics as they relate to head and neck cancer.

Oncolytic-adenovirus-expressed RNA interference for cancer therapy

IMPORTANCE OF THE FIELD

RNA interference (RNAi) has generated considerable excitement for its potential cancer therapeutic applications. Because of the difficulties in delivering a large amount of siRNA to cancer cells and the short half-life of siRNA, it is important to choose an efficient delivery system for transduction of siRNA into target cells. Oncolytic adenovirus offers a better platform by virtue of its high transfection efficiency and selective replication in cancer cells.

AREAS COVERED IN THIS REVIEW

This review focuses on the synergism between oncolytic adenovirus and siRNA antitumor responses, and discusses recent progresses in oncolytic-adenovirus-expressed siRNA.

WHAT THE READER WILL GAIN

siRNA-expressing oncolytic adenovirus can generate a significantly enhanced antitumor effect through gene knockdown and viral oncolysis.

TAKE HOME MESSAGE

Due to its potency and target specificity, using siRNA delivery by oncolytic adenovirus has generated much excitement and will open new avenues for treatment of human cancer.

Oncolytic herpes simplex virus vectors and chemotherapy: are combinatorial strategies more effective for cancer?

Despite aggressive treatments, including chemotherapy and radiotherapy, cancers often recur owing to resistance to conventional therapies. Oncolytic viruses such as oncolytic herpes simplex virus (oHSV) represent an exciting biological approach to cancer therapy. A range of viral mutations has been engineered into HSV to engender oncolytic activity. While oHSV as a single agent has been tested in a number of cancer clinical trials, preclinical studies have demonstrated enhanced efficacy when it is combined with cytotoxic anticancer drugs. Among the strategies that will be discussed in this article are combinations with standard-of-care chemotherapeutics, expression of prodrug-activating enzymes to enhance chemotherapy and small-molecule inhibitors. The combination of oHSV and chemotherapy can achieve much more efficient cancer cell killing than either single agent alone, often through synergistic interactions. This can be clinically important not just for improving efficacy but also for permitting lower and less toxic chemotherapeutic doses. The viral mutations in an oHSV vector often determine the favorability of its interactions with chemotherapy, just as different cancer cells, due to genetic alterations, vary in their response to chemotherapy. As chemotherapeutics are often the standard of care, combining them with an investigational new drug, such as oHSV, is clinically easier than combining multiple novel agents. As has become clear for most cancer therapies, multimodal treatments are usually more effective. In this article, we will discuss the recent progress of these combinatorial strategies between virotherapy and chemotherapy and future directions.

A phase I study of telomerase-specific replication competent oncolytic adenovirus (telomelysin) for various solid tumors

A phase I clinical trial was conducted to determine the clinical safety of Telomelysin, a human telomerase reverse transcriptase (hTERT) promoter driven modified oncolytic adenovirus, in patients with advanced solid tumors. A single intratumoral injection (IT) of Telomelysin was administered to three cohorts of patients (1 x 10(10), 1 x 10(11), 1 x 10(12) viral particles). Safety, response and pharmacodynamics were evaluated. Sixteen patients with a variety of solid tumors were enrolled. IT of Telomelysin was well tolerated at all dose levels. Common grade 1 and 2 toxicities included injection site reactions (pain, induration) and systemic reactions (fever, chills). hTERT expression was demonstrated at biopsy in 9 of 12 patients. Viral DNA was transiently detected in plasma in 13 of 16 patients. Viral DNA was detectable in four patients in plasma or sputum at day 7 and 14 post-treatment despite below detectable levels at 24 h, suggesting viral replication. One patient had a partial response of the injected malignant lesion. Seven patients fulfilled Response Evaluation Criteria in Solid Tumors (RECIST) definition for stable disease at day 56 after treatment. Telomelysin was well tolerated. Evidence of antitumor activity was suggested.

Bystander or no bystander for gene directed enzyme prodrug therapy

Gene directed enzyme prodrug therapy (GDEPT) of cancer aims to improve the selectivity of chemotherapy by gene transfer, thus enabling target cells to convert nontoxic prodrugs to cytotoxic drugs. A zone of cell kill around gene-modified cells due to transfer of toxic metabolites, known as the bystander effect, leads to tumour regression. Here we discuss the implications of either striving for a strong bystander effect to overcome poor gene transfer, or avoiding the bystander effect to reduce potential systemic effects, with the aid of three successful GDEPT systems. This review concentrates on bystander effects and drug development with regard to these enzyme prodrug combinations, namely herpes simplex virus thymidine kinase (HSV-TK) with ganciclovir (GCV), cytosine deaminase (CD) from bacteria or yeast with 5-fluorocytodine (5-FC), and bacterial nitroreductase (NfsB) with 5-(azaridin-1-yl)-2,4-dinitrobenzamide (CB1954), and their respective derivatives.

Oncolytic viruses from the perspective of the immune system

Cancer treatment with oncolytic viruses is at a crucial intersection from where two very different routes can be taken. The key role of the immune system needs to be addressed proactively to succeed. An immunocentric point of view posits that the intense immunosuppression induced by tumors can be outbalanced by the natural immunogenicity of viruses. To their advantage, viruses can be safely armed to be even more immunostimulatory. The microbe-associated inflammatory response is optimal for antigen presentation and helps to reveal the hidden tumor antigens. The induced immune effector cells patrol the organs to destroy disseminated tumor cells out of the reach of the oncolytic virus. However, as tumor immunosuppression is localized, this concept needs to be revisited because every tumor focus will have to be reached by the oncolytic virus. By contrast, virocentrics see the immune system as an obstacle to virotherapy. A virus is so immunogenic that it dominates all the elicited immunity to the detriment of a response towards tumor antigens. For them immunosuppression is the way to go, and the intense immunosuppression in and around the tumor is now an advantage, offering a privileged site for virus replication. A better oncolytic virus evades the immune system, but such a virus should be very tumor-selective to be safe. Although the trend favors immunocentrics, clinical results have been more often documented in immunocompromised patients. Trials of comparative interventions on the immune system will validate immunocentrism or virocentrism. What seems clear is that at this intersection one should take one route or the other to overcome the current limitations of virotherapy.

Targeted genetic and viral therapy for advanced head and neck cancers

Head and neck cancers usually present with advanced disease and novel therapies are urgently needed. Genetic therapy aims at restoring malfunctioned tumor suppressor gene(s) or introducing proapoptotic genes. Oncolytic virotherapeutics induce multiple cycles of cancer-specific virus replication, followed by oncolysis, virus spreading and infection of adjacent cancer cells. Oncolytic viruses can also be armed to express therapeutic transgene(s). Recent advances in preclinical and clinical studies are revealing the potential of both therapeutic classes for advanced head and neck cancers, including the approval of two products (Gendicine and H101) by a governmental agency. This review summarizes the available clinical data to date and discusses the challenges and future directions.

Gene medicine for cancer treatment: commercially available medicine and accumulated clinical data in China

Loss of p53 function compromises genetic homeostasis, which induces deregulated DNA replication, damages DNA, and subsequently results in increased resistance to anticancer agents. Pharmacological approaches using recombinant adenoviruses (Ad) have been developed to restore the p53 functions. Another approach for gene medicine is to modify Ad replication in a tumor-specific manner, which induces tumor cell death without damaging normal tissues in the vicinity. The Ad-derived gene medicines, Ad expressing the wild-type p53 gene and replication-competent Ad defective of the E1B-55kDa gene, have been tested for their clinical feasibility and became commercially available in China. These agents demonstrated their antitumor activities as a monotherapy and in combination with conventional chemotherapeutic agents. In this article, we summarize the outcomes of clinical trials in China, most of which have been published in domestic Chinese journals, and discuss potential directions of cancer gene therapy with these agents.

Oncolytic Viruses: A New Weapon to Fight Cancer

Remission from cancer after viral infection was first noted in the beginning of the 20th century, and with advances in virotherapy and genetic engineering, the advent of an approved viral therapeutic in North America is fast approaching. Mechanisms of tumour selectivity and killing, along with information obtained from clinical trials are reviewed here. Although oncolytic viruses are generally safe and well tolerated, their overall anti-tumour efficacy has varied. This article outlines strategies to improve the efficacy of the oncolytic platform without compromising its impressive safety profile. It will highlight new methods being developed to quantify the activity of oncolytic viruses in real time. Harnessing the factors that control the tumour microenvironment and the immune system are the key to enhancing the oncolytic activity. The purpose of this article is to introduce and provide an overview of the current state of cancer killing of oncolytic viruses. The reader will acquire knowledge of the basic principles of oncolytic viruses and their use in the clinical setting. This review summarizes articles retrieved from Medline using key words such as "virus," "oncolytic virus," "virotherapy," "cancer," and "clinical trials." Review articles published in the English language from 2005 onward were read and corroborating data and conclusions were summarized. When appropriate, cited references were also reviewed and incorporated. The reader is directed to references we found most concise.

Apoptosis: a relevant tool for anticancer therapy

Apoptosis is a form of cell death that permits the removal of damaged, senescent or unwanted cells in multicellular organisms, without damage to the cellular microenvironment. Defective apoptosis represents a major causative factor in the development and progression of cancer. The majority of chemotherapeutic agents, as well as radiation, utilize the apoptotic pathway to induce cancer cell death. Resistance to standard chemotherapeutic strategies also seems to be due to alterations in the apoptotic pathway of cancer cells. Recent knowledge on apoptosis has provided the basis for novel targeted therapies that exploit apoptosis to treat cancer. These new target include those acting in the extrinsic/intrinsic pathway, proteins that control the apoptosis machinery such as the p53 and proteosome pathway. Most of these forms of therapy are still in preclinical development because of their low specifity and susceptibility to drug resistance, but several of them have shown promising results. In particular, this review specifically aims at providing an update of certain molecular players that are already in use in order to target apoptosis (such as bortezomib) or which are still being clinically evaluated (such ONYX-015, survivin and exisulind/aptosyn) or which, following preclinical studies, might have the necessary requirements for becoming part of the anticancer drug programs (such as TRAIL/Apo2L, apoptin/VP3).

Intratumoral injection of inactivated Sendai virus particles elicits strong antitumor activity by enhancing local CXCL10 expression and systemic NK cell activation

We have already demonstrated that inactivated, replication-defective Sendai virus particles (HVJ-E) have a powerful antitumor effect by both the generation of tumor-specific cytotoxic T cells and inhibition of regulatory T cell activity. Here, we report that HVJ-E also has an antitumor effect through non-T cell immunity. Microarray analysis revealed that direct injection of HVJ-E induced the expression of CXCL10 in established Renca tumors. CXCL10 was secreted by dendritic cells in the tumors after HVJ-E injection. Quantitative real-time RT-PCR and immunohistochemistry revealed that CXCR3+ cells (predominantly NK cells) infiltrated the HVJ-E-injected tumors. Moreover, HVJ-E injection caused systemic activation of NK cells and enhanced their cytotoxity against tumor cells. In an in vivo experiment, approximately 50% of tumors were eradicated by HVJ-E injection, and this activity of HVJ-E against Renca tumors was largely abolished by NK cell depletion using anti-asialo GM1 antibody. Since HVJ-E injection induced systemic antitumor immunity by enhancing or correcting the chemokine-chemokine receptor axis, it might be a potential new therapy for cancer.

Comparison of adenoviruses from species B, C, E, and F after intravenous delivery

Recent attempts to circumvent the limitations of adenovirus (Ad) vectors derived from species C serotype Ad5 have focused on the use of alternative human serotypes. These new serotypes have multiple benefits including a low prevalence of neutralizing antibodies in humans and alternate tropisms. To investigate the characteristics of alternatives to Ad5 vectors, we compared the biodistribution and safety of Ads from species B (Ad3, 11p, 35), C (Ad5), E (Ad4), and F (Ad41), or chimeric Ad5 viruses containing the Ad11 or Ad35 fibers (Ad5/11 and Ad5/35), after intravenous (IV) delivery into hCD46 transgenic mice. Our data suggest that (i) mechanisms of cell and tissue sequestration differ; (ii) levels of sequestration to lung, liver, or spleen do not correlate with toxicity; (iii) delivery of all serotypes causes activation of coagulation, possibly through platelet interaction; (iv) despite binding to the same receptor in vitro, Ad serotypes act differently in vivo; and (v) platelet depletion affects blood clearance, organ sequestration and chemokine/cytokine release of some, but not all Ad serotypes. Overall, our data indicate that Ad5-based vectors are relatively safe as compared to other serotypes. This data should be taken into consideration in future studies about the clinical use of Ad vectors.

A new therapy for highly effective tumor eradication using HVJ-E combined with chemotherapy

BACKGROUND

Inactivated HVJ (hemagglutinating virus of Japan; Sendai virus) particles (HVJ envelope vector; HVJ-E can incorporate and deliver plasmid DNA, siRNA, antibody and peptide and anti-cancer drugs to cells both in vitro and in vivo. We attempted to eradicate tumors derived from mouse colon cancer cells, CT26, by combining bleomycin (BLM)-incorporated HVJ-E (HVJ-E/BLM) with cisplatin (CDDP) administration.

METHODS

CT-26 tumor mass was intradermally established in Balb/c mice. HVJ-E/BLM was directly injected into the tumor mass with or without intraperitoneal administration of CDDP. The anti-tumor effect was evaluated by measuring tumor size and cytotoxic T cell activity against CT26. Re-challenge of tumor cells to treated mice was performed 10 days or 8 months after the initial tumor inoculation.

RESULTS

We found that three intratumoral injections of HVJ-E/BLM along with a single intraperitoneal administration of CDDP eradicated CT26 tumors with more than 75% efficiency. When tumor cells were intradermally re-injected on day 10 after the initial tumor inoculation, tumors on both sides disappeared in most of the mice that received the combination therapy of HVJ-E/BLM and CDDP. Eight months after the initial tumor eradication, surviving mice were re-challenged with CT26 cells. The re-challenged tumors were rejected in all of the surviving mice treated with the combination therapy. Cytotoxic T lymphocytes specific for CT26 were generated in these surviving mice.

CONCLUSION

Combination therapy consisting of HVJ-E and chemotherapy completely eradicated the tumor, and generated anti-tumor immunity. The combination therapy could therefore be a promising new strategy for cancer therapy.

A phase I trial of intravenous infusion of ONYX-015 and enbrel in solid tumor patients

ONYX-015 is an attenuated chimeric human group C adenovirus, which preferentially replicates in and lyses tumor cells that are p53 negative. The purpose of this phase I, dose-escalation study was to determine the safety and feasibility of intravenous infusion with ONYX-015 in combination with enbrel in patients with advanced carcinoma. Enbrel is a recombinant dimer of human tumor-necrosis factor (TNF)-alpha receptor, previously shown to reduce the level of functional TNF. Nine patients, three in each cohort received multiple cycles of ONYX-015 infusion (1 x 10(10), 1 x 10(11) and 1 x 10(12) vp weekly for 4 weeks/cycle) in addition to subcutaneous enbrel (only during cycle 1) injections per FDA-indicated dosing. Of the nine patients, four had stable disease. No significant adverse events were attributed to the experimental regimen, confirming that enbrel can be safely administered along with oncolytic virotherapy. Two of the three patients in cohort 3 had detectable viral DNA at days 3 and 8 post-ONYX-015 infusion. Their detectable circulating viral DNA was markedly higher during cycle 1 (with enbrel coadministration) as compared with cycle 2 (without enbrel) at the same time points. Area under the curve determinations indicate a marked higher level of TNF-alpha induction and accelerated clearance at cycle 2 in the absence of enbrel. Further assessment is recommended.

Systemic efficacy of oncolytic adenoviruses in imagable orthotopic models of hormone refractory metastatic breast cancer

Conditionally replicating oncolytic adenoviruses represent a promising developmental strategy for the treatment of cancer refractory to current treatments, such as hormone refractory metastatic breast cancer. In clinical cancer trials, adenoviral agents have been well tolerated, but gene transfer has been insufficient for clinical benefit. One of the main reasons may be the deficiency of the primary adenovirus receptor, and therefore viral capsid modifications have been employed. Another obstacle to systemic delivery is rapid clearance of virus by hepatic Kupffer cells and subsequent inadequate bioavailability. In this study, we compared several capsid-modified oncolytic adenoviruses for the treatment of breast cancer with and without Kupffer cell inactivation. Replication deficient capsid-modified viruses were analyzed for their gene transfer efficacy in vitro in breast cancer cell lines and clinical samples and in vivo in orthotopic models of breast cancer. The effect of Kupffer cell depleting agents on gene transfer efficacy in vivo was evaluated. An aggressive lung metastatic model was developed to study the effect of capsid-modified oncolytic adenoviruses on survival. Capsid-modified viruses displayed increased gene transfer and cancer cell killing in vitro and resulted in increased survival in an orthotopic model of lung metastatic breast cancer in mice. Biodistribution of viruses was favorable, tumor burden and treatment response could be monitored repeatedly. Kuppfer cell inactivation led to enhanced systemic gene delivery, but did not increase the survival of mice. These results facilitate clinical translation of oncolytic adenoviruses for the treatment of hormone refractory metastatic breast cancer.

Clinical trial results with oncolytic virotherapy: a century of promise, a decade of progress

Therapeutic oncolytic viruses (virotherapeutics) constitute a novel class of targeted anticancer agents that have unique mechanisms of action compared with other cancer therapeutics. The development of virotherapeutics has evolved from the use of in vitro-passaged strains (first generation), to genetically engineered selectivity-enhanced viruses (second generation) and finally to genetically engineered transgene-expressing 'armed' oncolytic viruses (third generation). Descriptions of cancer remissions following virus infections date back to a century ago. Initial patient treatment publications, written up to 50 years ago, consisted of case reports or case series of treatment with first-generation, non-engineered viruses. Over the past decade, hundreds of patients with cancer have been treated on prospectively designed clinical trials (including phase III), evaluating over 10 different agents, inlcluding engineered second-generation and third-generation viruses. This Review summarizes and interprets the data from clinical reports over the last century, including safety, efficacy and biological end points (viral and immunologic). Systemic safety and efficiacy has been clearly demonstrated with some virotherapeutics. The implications of these data for future virotherapy development are discussed.

Recent clinical progress in virus-based therapies for cancer

As our knowledge of the molecular basis of cancer expands, viral vectors have been increasingly studied as potential antitumour therapeutic agents. With their ability to invade and replicate within target cells, viruses have been utilised as oncolytic agents to directly lyse tumour cells. Viruses can also deliver their genetic payload into infected cells, allowing for the repair of defective tumour suppressor genes, disruption of oncogenic pathways, and production of cytokines that activate the immune system. Finally, viruses encoding tumour-associated antigens can infect dendritic cells, triggering the development of a tumour-specific immune response. The ability to engineer viruses with high levels of tumour specificity and efficient rates of infection has enhanced the safety profile of these agents, allowing for the development of viable therapeutic options that have been examined in the clinic, either alone or in conjunction with more conventional therapies. This review highlights the principles underlying virus-based therapies for cancer, with an emphasis on recent developments from the clinic.

Biological activities of a recombinant adenovirus p53 (SCH 58500) administered by hepatic arterial infusion in a Phase 1 colorectal cancer trial

The major focus of intrahepatic arterial (IHA) administration of adenoviruses (Ad) has been on safety. Currently, there is little published data on the biological responses to Ad when administered via this route. As part of a Phase I study, we evaluated biological responses to a replication-defective adenovirus encoding the p53 transgene (SCH 58500) when administered by hepatic arterial infusion to patients with primarily colorectal cancer metastatic to the liver. In analyzing biological responses to the Ad vector, we found that both total and neutralizing Ad antibodies increased weeks after SCH 58500 infusion. The fold increase in antibody titers was not dependent on SCH 58500 dosage. The proinflammatory cytokine interleukin-6 (IL-6) transiently peaked within 6 h of dosing. The cytokine sTNF-R2 showed elevation by 24 h post-treatment, and fold increases were directly related to SCH 58500 doses. Cytokines TNF-alpha, IL-1beta, and sTNF-R1 showed no increased levels over 24 h. Predose antibody levels did not appear to predict transduction, nor did serum Ad neutralizing factor (SNF). Delivery of SCH 58500 to tumor tissue occurred, though we found distribution more predominantly in liver tissues, as opposed to tumors. RT-PCR showed significantly higher expression levels (P<0.0001, ANOVA) for adenovirus type 2 and 5 receptor (CAR) in liver tissues, suggesting a correlation with transduction. Evidence of tumor-specific apoptotic activity was provided by laser scanning cytometry, which determined a coincidence of elevated nuclear p53 protein expression with apoptosis in patient tissue. IHA administration of a replication defective adenovirus is a feasible mode of delivery, allowing for exogenous transfer of the p53 gene into target tissues, with evidence of functional p53. Limited and transient inflammatory responses to the drug occurred, but pre-existing immunity to Ad did not preclude SCH 58500 delivery.

Construction of doxycyline-dependent mini-HIV-1 variants for the development of a virotherapy against leukemias

T-cell acute lymphoblastic leukemia (T-ALL) is a high-risk type of blood-cell cancer. We describe the improvement of a candidate therapeutic virus for virotherapy of leukemic cells. Virotherapy is based on the exclusive replication of a virus in leukemic cells, leading to the selective removal of these malignant cells. To improve the safety of such a virus, we constructed an HIV-1 variant that replicates exclusively in the presence of the nontoxic effector doxycycline (dox). This was achieved by replacement of the viral TAR-Tat system for transcriptional activation by the Escherichia coli-derived Tet system for inducible gene expression. This HIV-rtTA virus replicates in a strictly dox-dependent manner. In this virus, additional deletions and/or inactivating mutations were introduced in the genes for accessory proteins. These proteins are essential for virus replication in untransformed cells, but dispensable in leukemic T cells. These minimized HIV-rtTA variants contain up to 7 deletions/inactivating mutations (TAR, Tat, vif, vpR, vpU, nef and U3) and replicate efficiently in the leukemic SupT1 T cell line, but do not replicate in normal peripheral blood mononuclear cells. These virus variants are also able to efficiently remove leukemic cells from a mixed culture with untransformed cells. The therapeutic viruses use CD4 and CXCR4 for cell entry and could potentially be used against CXCR4 expressing malignancies such as T-lymphoblastic leukemia/lymphoma, NK leukemia and some myeloid leukemias.

Viral Vaccines for Cancer Immunotherapy

The understanding that tumor cells can be recognized and eliminated by the immune system has led to intense interest in the development of cancer vaccines. Viruses are naturally occurring agents that cause human disease but have the potential to prevent disease when attenuated forms or subunits are used as vaccines before exposure. A large number of viruses have been engineered as attenuated vaccines for the expression of tumor antigens, immunomodulatory molecules, and as vehicles for direct destruction of tumor cells or expression of highly specific gene products. This article focuses on the major viruses that are under development as cancer vaccines, including the poxviruses, adenoviruses, adeno-associated viruses, herpesviruses, retroviruses, and lentiviruses. The biology supporting these viruses as vaccines is reviewed and clinical progress is reported.

Cancer scene investigation: how a cold virus became a tumor killer

Oncolytic therapy is a novel anticancer treatment with attenuated lytic viruses such as adenovirus (Ad). These viruses kill the host cells through their lytic replication cycle and are thus distinct from classical gene therapy viruses, which serve as gene delivery agents and do not replicate. Oncolytic Ads are genetically engineered so as to replicate only in cancer cells. Their replication cycle leads to viral multiplication, the killing of the host cells and spreading of the infection throughout the tumor. Following success in preclinical studies, their anti-tumor potential is now being evaluated in the clinic. Three oncolytic Ads (dl1520, Ad5-CD/TKrep, and CV706) have completed Phase I and II clinical trials in cancer patients where their administration via multiple routes and in combination with chemo- or radiotherapies, has demonstrated overall safety. These viruses are being re-engineered to arm them with additional therapeutic genes, bolstering their oncolytic activity with a bystander effect. For example, Ad5-CD/TKrep delivers a therapeutic prodrug-activating (suicide) gene. These data indicate that oncolytic Ads are a promising novel cancer treatment approach that can be combined with other modalities, such as gene therapy and classical chemo- and radiotherapies. Further improvements to enhance their specificity, targeting and oncolytic activity are needed however, as these first-generation viruses showed modest anti-tumor activity. To improve their efficacy in the clinic, it will be important to devise and incorporate novel monitoring techniques in the clinical trials, such as analysis of viral replication in biopsies and through the use of creative noninvasive imaging technologies.

p53 as a target for anti-cancer drug development

Loss of p53 function compromises genetic homeostasis in cells exhibiting deregulated DNA replication and/or DNA damage, and prevents normal cytotoxic responses to cancer therapies. Genetic and pharmacological approaches are being developed with the ultimate goal of restoring or controlling p53 functions in cancer patients. Progress has recently been made in the clinical use of replication-deficient virus carrying wt-TP53 (Ad5CMV-p53) and/or cancer-selective oncolytic adenoviruses (ONYX-015). These strategies demonstrated clinical activity as monotherapy and were synergistic with traditional chemotherapy agents in the treatment of some types of cancer. In addition, pharmacological methods are under development to either stimulate wild-type p53 protein function, or induce p53 mutant proteins to resume wild-type functions. These methods are based on small chemicals (CP-31388, PRIMA-1), peptides (CDB3) or single-chain Fv antibody fragments corresponding to defined p53 domains. Here, we discuss the mechanisms underlying these approaches and their perspectives for cancer therapy.

A Phase 1 Clinical Study of Intravenous Administration of PV701, an Oncolytic Virus, Using Two-Step Desensitization

PURPOSE

In a previous phase 1 study, adverse events, especially flu-like symptoms, were observed mainly following the first i.v. bolus dose of PV701, an oncolytic Newcastle disease virus. Desensitization to adverse events of subsequent doses occurred, allowing a 10-fold increase in the maximum tolerated dose for these doses. Although one-step desensitization (a single desensitizing dose with higher subsequent doses) addressed the tolerability of high repeat doses, additional testing was required to further improve tolerability of the initial dose. This study tested the hypothesis that two-step desensitization, using two dose increments before high repeat doses, would be well tolerated.

EXPERIMENTAL DESIGN

Sixteen adults with incurable solid tumors were enrolled. Cycles consisted of six PV701 doses over 2 weeks followed by a 1-week rest. Doses 1 to 2 were 1 and 12 x 10(9) plaque-forming units (pfu)/m(2), respectively, whereas doses 3 to 6 were escalated by cohort from 24 to 120 x 10(9) pfu/m(2).

RESULTS

No dose-limiting toxicities were observed, permitting dose escalation through cohort 4 (1, 12, 120, 120, 120, 120 x 10(9) pfu/m(2)). Mild flu-like symptoms were common following the first infusion, diminished with repeated dosing, and were less pronounced than those seen previously. Tumor regression was observed in a patient with anal carcinoma who enrolled with stable disease following palliative radiotherapy. Four patients with clearly progressing cancer before enrollment had disease stabilization of >/=6 months.

CONCLUSIONS

This novel two-step desensitization improved patient tolerability compared with the previous regimen. Toxicities were predictable and manageable. PV701, the first oncolytic virus to enter phase 1 i.v. testing, continues to show single-agent activity, warranting planned phase 2 trials.

Oncolytic virotherapy for cancer treatment: challenges and solutions

Advances in gene modification and viral therapy have led to the development of a variety of vectors in several viral families that are capable of replication specifically in tumor cells. Because of the nature of viral delivery, infection, and replication, this technology, oncolytic virotherapy, may prove valuable for treating cancer patients, especially those with inoperable tumors. Current limitations exist, however, for oncolytic virotherapy. They include the body's B and T cell responses, innate inflammatory reactions, host range, safety risks involved in using modified viruses as treatments, and the requirement that most currently available oncolytic viruses require local administration. Another important constraint is that genetically enhanced vectors may or may not adhere to their replication restrictions in long-term applications. Several solutions and strategies already exist, however, to minimize or circumvent many of these limitations, supporting viral oncolytic therapy as a viable option and powerful tool in the fight against cancer.

Individualised cancer therapeutics: dream or reality? Therapeutics construction

The analysis of DNA microarray and proteomic data, and the subsequent integration into functional expression sets, provides a circuit map of the hierarchical cellular networks responsible for sustaining the viability and environmental competitiveness of cancer cells, that is, their robust systematics. These technologies can be used to 'snapshot' the unique patterns of molecular derangements and modified interactions in cancer, and allow for strategic selection of therapeutics that best match the individual profile of the tumour. This review highlights technology that can be used to selectively disrupt critical molecular targets and describes possible vehicles to deliver the synthesised molecular therapeutics to the relevant cellular compartments of the malignant cells. RNA interference (RNAi) involves a group of evolutionarily conserved gene silencing mechanisms in which small sequences of double-stranded RNA or intrinsic antisense RNA trigger mRNA cleavage or translational repression, respectively. Although RNAi molecules can be synthesised to 'silence' virtually any gene, even if upregulated, a mechanism for selective delivery of RNAi effectors to sites of malignant disease remains challenging. The authors will discuss gene-modified conditionally replicating viruses as candidate vehicles for the delivery of RNAi.

Oncolytic viral therapies – the clinical experience

It has been 9 years since the beginning of the first clinical trial in which an oncolytic virus was administered to cancer patients. Since then, oncolytic viruses from five different species have been taken to phase I and II clinical trials in over 300 cancer patients. While additional studies will be required to ascertain if the efficacy of any of these agents is high enough to warrant adding them to the existing therapeutic regimen, it has been reassuring that DNA viruses engineered to achieve tumor selectivity and RNA viruses with relative inherent natural tumor selectivity have proven reasonably safe at the wide range of doses that were tested. Here, we review the biology and clinical results of these five species of viruses and discuss lessons learned and challenges for the future.

Construction of a minimal HIV-1 variant that selectively replicates in leukemic derived T-cell lines: towards a new virotherapy approach

T-cell acute lymphoblastic leukemia is a high-risk type of blood-cell cancer. We analyzed the possibility of developing virotherapy for T-cell acute lymphoblastic leukemia. Virotherapy is based on the exclusive replication of a virus in leukemic cells, leading to the selective removal of these malignant cells. We constructed a minimized derivative of HIV-1, a complex lentivirus encoding multiple accessory functions that are essential for virus replication in untransformed cells, but dispensable in leukemic T cells. This mini-HIV virus has five deletions (vif, vpR, vpU, nef, and U3) and replicated in the SupT1 cell line, but did not replicate in normal peripheral blood mononuclear cells. The stripped down mini-HIV variant was also able to efficiently remove leukemic cells from a mixed culture with untransformed control cells. In contrast to wild-type HIV-1, we did not observe bystander killing in mixed culture experiments with the mini-HIV variant. Furthermore, viral escape was not detected in long-term cultures. The mini-HIV variant that uses CD4 and CXCR4 for cell entry could potentially be used against CXCR4-expressing malignancies such as T-lymphoblastic leukemia/lymphoma, natural killer leukemia, and some myeloid leukemias.