Long-term follow-up of patients with malignant pleural mesothelioma receiving high-dose adenovirus herpes simplex thymidine kinase/ganciclovir suicide gene therapy

Telomeres and telomerase in mesothelioma: Pathophysiology, biomarkers and emerging therapeutic strategies (Review)

Malignant mesothelioma (MM) is a rare but aggressive cancer linked to asbestos exposure and characterized by advanced‑stage disease at presentation. Despite advances in treatment, prognosis remains abysmal, highlighting the imperative for the development of novel biomarkers and treatment approaches. Telomere biology plays a pivotal role in the tumorigenic process and has emerged as a key area in oncology research. Short telomeres have been associated with genomic instability, and substantially shorter telomere length (TL) has been identified in MM, showcasing the potential of TL in risk assessment, early detection, and disease progression monitoring. MM predominantly maintains TL through telomerase activity (TA), which in research has been identified in >90% of MM cases, underscoring the potential of TA as a biomarker in MM. Telomerase reverse transcriptase (TERT) polymorphisms may serve as valuable biomarkers, with research identifying associations between single nucleotide polymorphisms (SNPs) and the risk and prognosis of MM. Additionally, TERT promoter mutations have been associated with poor prognosis and advanced‑stage disease, with the non‑canonical functions of TERT hypothesized to contribute to the development of MM. TERT promoter mutations occur in ~12% of MM cases; C228T, C250T and A161C are the most common, while the distribution and frequency differ depending on histological subtype. Research reveals the promise of the various approaches therapeutically targeting telomerase, with favorable results in pre‑clinical models and inconclusive findings in clinical trials. The present review examines the role of telomere biology in MM and its implications in diagnosis, prognosis, and therapy.

In Situ Tumor Vaccination Using Lipid Nanoparticles to Deliver Interferon-β mRNA Cargo

Background: In situ cancer vaccination is a therapeutic approach that involves stimulating the immune system in order to generate a polyclonal, anti-tumor response against an array of tumor neoantigens. Traditionally, in situ vaccination approaches have utilized adenoviral vectors to deliver immune-stimulating genes directly to the tumor microenvironment. Lipid nanoparticle (LNP)-mediated delivery methods offer several advantages over adenoviral delivery approaches, including increased safety, repeated administration potential, and enhanced tumor microenvironment activation. Methods: To explore in situ vaccination using LNPs, we evaluated LNP-mediated delivery of a reporter gene, mCherry, and an immune-stimulating gene, IFNβ, in several in vitro and in vivo models of lung cancer. Results: In vitro experiments demonstrated successful transfection of murine cancer cell lines with LNPs carrying both mCherry and IFN-β mRNA, resulting in high expression levels and IFNβ production. In vivo studies using LLC.ova flank tumors showed that intratumoral injection of IFNβ-mRNA LNPs led to significant IFNβ production within the tumor microenvironment, with minimal systemic exposure. Therapeutic efficacy was evaluated by injecting established LLC.ova flank tumors with IFNβ-mRNA LNPs bi-weekly for two weeks. Treated tumors showed significant growth inhibition compared to controls. Flow cytometric analysis of tumor-infiltrating leukocytes revealed that tumors injected with IFNβ-mRNA LNPs were associated with an increased CD8:CD4 T-cell ratio among lymphocytes, more CD69-expressing CD8 T-cells, and an increased presence of M1 macrophages. Efficacy and an abscopal effect were confirmed in a squamous cell carcinoma model, MOC1. No toxicity was observed. Conclusions: These findings show that intratumoral LNP delivery of immune-stimulating mRNA transcripts, such as IFNβ, can effectively stimulate local anti-tumor immune responses and warrants further investigation as a potential immunotherapeutic approach for cancer.

Current Status and Challenges of Oncolytic Virotherapy for the Treatment of Glioblastoma

Despite decades of research and numerous clinical trials, the prognosis of patients diagnosed with glioblastoma (GBM) remains dire with median observed survival at 8 months. There is a critical need for novel treatments for GBM, which is the most common malignant primary brain tumor. Major advances in cancer therapeutics such as immune checkpoint inhibitors and chimeric antigen receptor (CAR) T-cell therapy have not yet led to improved outcomes for GBM. Conventional therapy of surgery followed by chemoradiation with or without tumor treating fields remains the standard of care. One of the many approaches to GBM therapy currently being explored is viral therapies. These typically work by selectively lysing target neoplastic cells, called oncolysis, or by the targeted delivery of a therapeutic transgene via a viral vector. In this review, we discuss the underlying mechanisms of action and describe both recent and current human clinical trials using these viruses with an emphasis on promising viral therapeutics that may ultimately break the field's current stagnant paradigm.

Correlative analysis from a phase I clinical trial of intrapleural administration of oncolytic vaccinia virus (Olvi-vec) in patients with malignant pleural mesothelioma

Background

The attenuated, genetically engineered vaccinia virus has been shown to be a promising oncolytic virus for the treatment of patients with solid tumors, through both direct cytotoxic and immune-activating effects. Whereas systemically administered oncolytic viruses can be neutralized by pre-existing antibodies, locoregionally administered viruses can infect tumor cells and generate immune responses. We conducted a phase I clinical trial to investigate the safety, feasibility and immune activating effects of intrapleural administration of oncolytic vaccinia virus (NCT01766739).

Methods

Eighteen patients with malignant pleural effusion due to either malignant pleural mesothelioma or metastatic disease (non-small cell lung cancer or breast cancer) underwent intrapleural administration of the oncolytic vaccinia virus using a dose-escalating method, following drainage of malignant pleural effusion. The primary objective of this trial was to determine a recommended dose of attenuated vaccinia virus. The secondary objectives were to assess feasibility, safety and tolerability; evaluate viral presence in the tumor and serum as well as viral shedding in pleural fluid, sputum, and urine; and evaluate anti-vaccinia virus immune response. Correlative analyses were performed on body fluids, peripheral blood, and tumor specimens obtained from pre- and post-treatment timepoints.

Results

Treatment with attenuated vaccinia virus at the dose of 1.00E+07 plaque-forming units (PFU) to 6.00E+09 PFU was feasible and safe, with no treatment-associated mortalities or dose-limiting toxicities. Vaccinia virus was detectable in tumor cells 2-5 days post-treatment, and treatment was associated with a decrease in tumor cell density and an increase in immune cell density as assessed by a pathologist blinded to the clinical observations. An increase in both effector (CD8+, NK, cytotoxic cells) and suppressor (Tregs) immune cell populations was observed following treatment. Dendritic cell and neutrophil populations were also increased, and immune effector and immune checkpoint proteins (granzyme B, perforin, PD-1, PD-L1, and PD-L2) and cytokines (IFN-γ, TNF-α, TGFβ1 and RANTES) were upregulated.

Conclusion

The intrapleural administration of oncolytic vaccinia viral therapy is safe and feasible and generates regional immune response without overt systemic symptoms.

Clinical trial registration

https://clinicaltrials.gov/ct2/show/NCT01766739, identifier NCT01766739.

A trial of intra-pleural bacterial immunotherapy in malignant pleural mesothelioma (TILT) - a randomised feasibility study using the trial within a cohort (TwiC) methodology

BACKGROUND

Malignant pleural mesothelioma (MPM) is an aggressive thoracic malignancy with a poor prognosis. Systemic immunotherapy is an effective frontline treatment for MPM, and there is a scientific rationale supporting the possible efficacy of local, i.e. intra-pleural immune modulators. Trial of intra-pleural bacterial immunotherapy (TILT) investigated the feasibility of performing a randomised trial of intra-pleural bacterial immunotherapy in people with MPM, using the trials within cohorts (TwiC) methodology.

METHODS

TILT was a multicentre, three-armed, randomised, feasibility TwiC of intra-pleural OK432, BCG, or usual care in people with MPM. Eligible participants were identified from within the ASSESS-meso study, a prospective, longitudinal, observational cohort study, and were randomly selected to be offered a single dose of OK432 or BCG, via an indwelling pleural catheter. The primary outcome was feasibility, evaluated against prespecified recruitment, attrition and data completeness targets. The acceptability of trial processes and interventions was assessed during qualitative interviews with participants and family members at the end of the trial. TILT was registered prospectively on the European Clinical Trials Registry (EudraCT number 2016-004,727-23) and the ISRCTN Register on 04 December 2017.

RESULTS

Seven participants were randomised from a planned sample size of 12; thus, the 66% recruitment rate target was not met. Two participants withdrew after randomisation, breaching the pre-stated attrition threshold of 10%. It was not possible to maintain blinding of control participants, which negated a fundamental tenet of the TwiC design. The trial processes and methodology were generally acceptable to participants and relatives, despite several recipients of intra-pleural bacterial agents experiencing significant local and systemic inflammatory responses.

CONCLUSION

It was possible to design a clinical trial of an investigational medicinal product based on the TwiC design and to obtain the necessary regulatory approvals. However, whilst acceptable to participants and relatives, the TwiC design was not a feasible method of investigating intra-pleural bacterial immunotherapy in people with MPM. Future trials investigating this topic should consider the eligibility constraints and recruitment difficulties encountered.

TRIAL REGISTRATION

TILT was registered prospectively on the European Clinical Trials Registry (EudraCT number 2016-004727-23 ) and the ISRCTN Register ( 10432197 ) on 04 December 2017.

Role of Adenoviruses in Cancer Therapy

Cancer is one of the leading causes of death in the world, which is the second after heart diseases. Adenoviruses (Ads) have become the promise of new therapeutic strategy for cancer treatment. The objective of this review is to discuss current advances in the applications of adenoviral vectors in cancer therapy. Adenoviral vectors can be engineered in different ways so as to change the tumor microenvironment from cold tumor to hot tumor, including; 1. by modifying Ads to deliver transgenes that codes for tumor suppressor gene (p53) and other proteins whose expression result in cell cycle arrest 2. Ads can also be modified to express tumor specific antigens, cytokines, and other immune-modulatory molecules. The other strategy to use Ads in cancer therapy is to use oncolytic adenoviruses, which directly kills tumor cells. Gendicine and Advexin are replication-defective recombinant human p53 adenoviral vectors that have been shown to be effective against several types of cancer. Gendicine was approved for treatment of squamous cell carcinoma of the head and neck by the Chinese Food and Drug Administration (FDA) agency in 2003 as a first-ever gene therapy product. Oncorine and ONYX-015 are oncolytic adenoviral vectors that have been shown to be effective against some types of cancer. The Chiness FDA agency has also approved Oncorin for the treatment of head and neck cancer. Ads that were engineered to express immune-stimulatory cytokines and other immune-modulatory molecules such as TNF-α, IL-2, BiTE, CD40L, 4-1BBL, GM-CSF, and IFN have shown promising outcome in treatment of cancer. Ads can also improve therapeutic efficacy of immune checkpoint inhibitors and adoptive cell therapy (Chimeric Antigen Receptor T Cells). In addition, different replication-deficient adenoviral vectors (Ad5-CEA, Ad5-PSA, Ad-E6E7, ChAdOx1-MVA and Ad-transduced Dendritic cells) that were tested as anticancer vaccines have been demonstrated to induce strong antitumor immune response. However, the use of adenoviral vectors in gene therapy is limited by several factors such as pre-existing immunity to adenoviral vectors and high immunogenicity of the viruses. Thus, innovative strategies must be continually developed so as to overcome the obstacles of using adenoviral vectors in gene therapy.

Nonreplicating Adenoviral Vectors: Improving Tropism and Delivery of Cancer Gene Therapy

Recent preclinical and clinical studies have used viral vectors in gene therapy research, especially nonreplicating adenovirus encoding strategic therapeutic genes for cancer treatment. Adenoviruses were the first DNA viruses to go into therapeutic development, mainly due to well-known biological features: stability in vivo, ease of manufacture, and efficient gene delivery to dividing and nondividing cells. However, there are some limitations for gene therapy using adenoviral vectors, such as nonspecific transduction of normal cells and liver sequestration and neutralization by antibodies, especially when administered systemically. On the other hand, adenoviral vectors are amenable to strategies for the modification of their biological structures, including genetic manipulation of viral proteins, pseudotyping, and conjugation with polymers or biological membranes. Such modifications provide greater specificity to the target cell and better safety in systemic administration; thus, a reduction of antiviral host responses would favor the use of adenoviral vectors in cancer immunotherapy. In this review, we describe the structural and molecular features of nonreplicating adenoviral vectors, the current limitations to their use, and strategies to modify adenoviral tropism, highlighting the approaches that may allow for the systemic administration of gene therapy.

Neoadjuvant Gene-Mediated Cytotoxic Immunotherapy for Non-Small-Cell Lung Cancer: Safety and Immunologic Activity

Gene-mediated cytotoxic immunotherapy (GMCI) is an immuno-oncology approach involving local delivery of a replication-deficient adenovirus expressing herpes simplex thymidine kinase (AdV-tk) followed by anti-herpetic prodrug activation that promotes immunogenic tumor cell death, antigen-presenting cell activation, and T cell stimulation. This phase I dose-escalation pilot trial assessed bronchoscopic delivery of AdV-tk in patients with suspected lung cancer who were candidates for surgery. A single intra-tumoral AdV-tk injection in three dose cohorts (maximum 1012 viral particles) was performed during diagnostic staging, followed by a 14-day course of the prodrug valacyclovir, and subsequent surgery 1 week later. Twelve patients participated after appropriate informed consent. Vector-related adverse events were minimal. Immune biomarkers were evaluated in tumor and blood before and after GMCI. Significantly increased infiltration of CD8+ T cells was found in resected tumors. Expression of activation, inhibitory, and proliferation markers, such as human leukocyte antigen (HLA)-DR, CD38, Ki67, PD-1, CD39, and CTLA-4, were significantly increased in both the tumor and peripheral CD8+ T cells. Thus, intratumoral AdV-tk injection into non-small-cell lung cancer (NSCLC) proved safe and feasible, and it effectively induced CD8+ T cell activation. These data provide a foundation for additional clinical trials of GMCI for lung cancer patients with potential benefit if combined with other immune therapies.

Oncolytic herpesvirus therapy for mesothelioma - A phase I/IIa trial of intrapleural administration of HSV1716

OBJECTIVES

Malignant Pleural Mesothelioma (MPM) remains a major oncological challenge with limited therapeutic options. HSV1716 is a replication restricted oncolytic herpes simplex virus with anti-tumor effects in multiple cell lines including MPM. Intrapleural treatment appeals because MPM is typically multifocal but confined to the pleura, and distant metastases are uncommon. We assessed the safety and possible efficacy of intrapleural HSV1716 for inoperable MPM.

MATERIALS AND METHODS

Patients with MPM received 1 × 10⁷iu HSV1716 injected via an indwelling intrapleural catheter (IPC) on one, two or four occasions a week apart. The primary endpoint was the safety and tolerability of HSV1716. Secondary endpoints were assessment of HSV1716 replication, detection of immune response and evaluation of tumor response.

RESULTS

Of thirteen patients enrolled, five had received previous pemetrexed-cisplatin chemotherapy, and eight were chemotherapy naïve. Three patients were enrolled to receive one dose, three patients to two doses and seven patients to four doses. The treatment was well-tolerated with few virus-related adverse events and no dose limiting toxicities. Twelve patients were evaluable for response, as one patient withdrew early after a catheter fracture. There was evidence of viral replication/persistence in pleural fluid in seven of the twelve patients. Induction of Th1 cytokine responses to HSV1716 treatment occurred in eight patients and four patients developed novel anti-tumor IgG. No objective responses were observed but disease stabilization was reported in 50 % of patients at 8 weeks.

CONCLUSIONS

Intrapleural HSV1716 was well-tolerated and demonstrated an anti-tumor immune response in MPM patients. These results provide a rationale for further studies with this agent in MPM and in combination with other therapies.

Immunotherapy for mesothelioma: a critical review of current clinical trials and future perspectives

At the clinical level the role of immunotherapy in cancer is currently at a pivotal point. Therapies such as checkpoint inhibitors are being approved at many levels in cancers such as non-small cell lung cancer (NSCLC). Mesothelioma is a rare orphan disease associated with prior exposure to asbestos, with a dismal prognosis. Various clinical trials for checkpoint inhibitors have been conducted in this rare disease, and suggest that such therapies may play a role as a treatment option for a proportion of patients with this cancer. Most recently approved as a salvage therapy in mesothelioma was granted in Japan, regulatory approval for their use in the clinic elsewhere lags. In this article we review the current pertinent clinical trials of immunotherapies in malignant mesothelioma, discuss the current issues that may affect the clinical outcomes of such therapies and further evaluate potential candidate new avenues that may become future targets for immunotherapy in this cancer.

Engineering and Characterization of Oncolytic Vaccinia Virus Expressing Truncated Herpes Simplex Virus Thymidine Kinase

Oncolytic viruses are a promising class of anti-tumor agents; however, concerns regarding uncontrolled viral replication have led to the development of a replication-controllable oncolytic vaccinia virus (OVV). The engineering involves replacing the native thymidine kinase (VV-tk) gene, in a Wyeth strain vaccinia backbone, with the herpes simplex virus thymidine kinase (HSV-tk) gene, which allows for viral replication control via ganciclovir (GCV, an antiviral/cytotoxic pro-drug). Adding the wild-type HSV-tk gene might disrupt the tumor selectivity of VV-tk deleted OVVs; therefore, only engineered viruses that lacked tk activity were selected as candidates. Ultimately, OTS-412, which is an OVV containing a mutant HSV-tk, was chosen for characterization regarding tumor selectivity, sensitivity to GCV, and the influence of GCV on OTS-412 anti-tumor effects. OTS-412 demonstrated comparable replication and cytotoxicity to VV^tk- (control, a VV-tk deleted OVV) in multiple cancer cell lines. In HCT 116 mouse models, OTS-412 replication in tumors was reduced by >50% by GCV (p = 0.004); additionally, combination use of GCV did not compromise the anti-tumor effects of OTS-412. This is the first report of OTS-412, a VV-tk deleted OVV containing a mutant HSV-tk transgene, which demonstrates tumor selectivity and sensitivity to GCV. The HSV-tk/GCV combination provides a safety mechanism for future clinical applications of OTS-412.

Scientific Advances and New Frontiers in Mesothelioma Therapeutics

Malignant pleural mesothelioma (MPM) is a rare and aggressive cancer that arises from the mesothelial surface of the pleural and peritoneal cavities, the pericardium, and rarely, the tunica vaginalis. The incidence of MPM is expected to increase worldwide in the next two decades. However, even with the use of multimodality treatment, MPM remains challenging to treat, with a 5-year survival rate of less than 5%. The International Association for the Study of Lung Cancer has gathered experts in different areas of mesothelioma research and management to summarize the most significant scientific advances and new frontiers related to mesothelioma therapeutics.

Phase I Study of Intrapleural Gene-Mediated Cytotoxic Immunotherapy in Patients with Malignant Pleural Effusion

Gene-mediated cytotoxic immunotherapy (GMCI) is an immune strategy implemented through local delivery of an adenovirus-based vector expressing the thymidine kinase gene (aglatimagene besadenovec, AdV-tk) followed by anti-herpetic prodrug valacyclovir. A phase I dose escalation trial of GMCI followed by chemotherapy was conducted in patients with malignant pleural effusion (MPE). AdV-tk was administered intrapleurally (IP) in three cohorts at a dose of 1 × 10¹² to 10¹³ vector particles. Primary endpoint was safety; secondary endpoints included response rate, progression-free survival, and overall survival. Nineteen patients were enrolled: median age 67 years; 14 with malignant mesothelioma, 4 non-small-cell lung cancer (NSCLC), and 1 breast cancer. There were no dose limiting toxicities. All 3 patients in cohort 2 experienced transient cytokine release syndrome (CRS). Addition of celecoxib in cohort 3 reduced the incidence and severity of CRS (none > grade 2). Three patients are alive (23-33 months after GMCI), and 3 of 4 NSCLC patients had prolonged disease stabilization; one is alive 29 months after GMCI, 3.6 years after initial diagnosis. GMCI was safe and well tolerated in combination with chemotherapy in patients with MPE and showed encouraging response. Further studies are warranted to determine efficacy.

Intracavitary Therapeutics for Pleural Malignancies

Pleural malignancies remain a serious therapeutic challenge, and are frequently refractory to standard treatment; however, they have the advantage of occurring in an enclosed cavity readily accessible for examination, biopsy, and serial sampling. Novel therapeutics can be administered via intracavitary delivery to maximize efficacy by targeting the site of involvement and potentially mitigating the adverse effects of systemic therapies. The easy accessibility of the pleural space lends itself well to repeated sampling and analysis to determine efficacy and toxicity of a given treatment paradigm. These factors support the rationale for delivery of novel therapeutics directly into the pleural space.

Advances in systemic therapy for malignant mesothelioma: future perspectives

Malignant mesothelioma is a rare and aggressive form of cancer affecting the mesothelium. This mainly occupational disease is becoming more common in those countries where asbestos has been used for industrial applications. Notwithstanding the progress made in the field, patients do not survive more than 12 months on average with standard treatment. With the advent of next generation sequencing, it is now possible to study the mutational landscape of each tumor with the aim of identifying the genetic aberrations driving tumorigenesis. This review encompasses the latest research in the field, with particular attention to new chemotherapy combinatorial regimens, molecular targets and immunotherapies, providing a comprehensive picture of the current and future treatment options for malignant mesothelioma patients.

Oncolytic Viral Therapy for Mesothelioma

The limited effectiveness of conventional therapy for malignant pleural mesothelioma demands innovative approaches to this difficult disease. Even with aggressive multimodality treatment of surgery, radiation, and/or chemotherapy, the median survival is only 1–2 years depending on stage and histology. Oncolytic viral therapy has emerged in the last several decades as a rapidly advancing field of immunotherapy studied in a wide spectrum of malignancies. Mesothelioma makes an ideal candidate for studying oncolysis given the frequently localized pattern of growth and pleural location providing access to direct intratumoral injection of virus. Therefore, despite being a relatively uncommon disease, the multitude of viral studies for mesothelioma can provide insight for applying such therapy to other malignancies. This article will begin with a review of the general principles of oncolytic therapy focusing on antitumor efficacy, tumor selectivity, and immune system activation. The second half of this review will detail results of preclinical models and human studies for oncolytic virotherapy in mesothelioma.

Genetic Modification of the Lung Directed Toward Treatment of Human Disease

Genetic modification therapy is a promising therapeutic strategy for many diseases of the lung intractable to other treatments. Lung gene therapy has been the subject of numerous preclinical animal experiments and human clinical trials, for targets including genetic diseases such as cystic fibrosis and α1-antitrypsin deficiency, complex disorders such as asthma, allergy, and lung cancer, infections such as respiratory syncytial virus (RSV) and Pseudomonas, as well as pulmonary arterial hypertension, transplant rejection, and lung injury. A variety of viral and non-viral vectors have been employed to overcome the many physical barriers to gene transfer imposed by lung anatomy and natural defenses. Beyond the treatment of lung diseases, the lung has the potential to be used as a metabolic factory for generating proteins for delivery to the circulation for treatment of systemic diseases. Although much has been learned through a myriad of experiments about the development of genetic modification of the lung, more work is still needed to improve the delivery vehicles and to overcome challenges such as entry barriers, persistent expression, specific cell targeting, and circumventing host anti-vector responses.

Overcoming barriers of car T-cell therapy in patients with mesothelin-expressing cancers

One obstacle to the application of immunotherapy to solid malignancies is to overcome the existing tolerance to self-antigens. Vaccine strategies aimed at harnessing endogenous antitumor T cells are limited by the T-cell receptor repertoire, which can be detected within the thymus as central tolerance or rendered nonfunctional by post-thymic mechanisms of peripheral tolerance. Adoptive immunotherapy can overcome these obstacles, since therapeutically effective T cells can be engineered to recognize tumors. Continued advancements in novel treatments, including immunotherapy, in solid malignancies are imperative. While mesothelin is an attractive target for cancer immunotherapy given its normal expression is limited to mesothelial cells, the breakthrough for chimeric antigen receptor T-cell treatment against this antigen is still forthcoming.

Promising investigational drug candidates in phase I and phase II clinical trials for mesothelioma

INTRODUCTION

Malignant mesothelioma is a rare and lethal malignancy primarily affecting the pleura and peritoneum. Mesothelioma incidence is expected to increase worldwide and current treatments remain ineffective, leading to poor prognosis. Within this article potential targets to improve the quality of life of the patients and assessment of further avenues for research are discussed. Areas covered: This review highlights emerging therapies currently under investigation for malignant mesothelioma with a specific focus on phase I and phase II clinical trials. Three main areas are discussed: immunotherapy (immune checkpoint blockade and cancer vaccines, among others), multitargeted therapy (such as targeting pro-angiogenic genes) and gene therapy (such as suicide gene therapy). For each, clinical trials are described to detail the current or past investigations at phase I and II. Expert opinion: The approach of applying existing treatments from other cancers does not show significant benefit, with the most promising outcome being an increase in survival of 2.7 months following combination of chemotherapy with bevacizumab. It is our opinion that the hypoxic microenvironment, the role of the stroma, and the metabolic status of mesothelioma should all be assessed and characterised to aid in the development of new treatments to improve patient outcomes.

Asbestos Induces Oxidative Stress and Activation of Nrf2 Signaling in Murine Macrophages: Chemopreventive Role of the Synthetic Lignan Secoisolariciresinol Diglucoside (LGM2605)

The interaction of asbestos fibers with macrophages generates harmful reactive oxygen species (ROS) and subsequent oxidative cell damage that are key processes linked to malignancy. Secoisolariciresinol diglucoside (SDG) is a non-toxic, flaxseed-derived pluripotent compound that has antioxidant properties and may thus function as a chemopreventive agent for asbestos-induced mesothelioma. We thus evaluated synthetic SDG (LGM2605) in asbestos-exposed, elicited murine peritoneal macrophages as an in vitro model of tissue phagocytic response to the presence of asbestos in the pleural space. Murine peritoneal macrophages (MFs) were exposed to crocidolite asbestos fibers (20 µg/cm²) and evaluated at various times post exposure for cytotoxicity, ROS generation, malondialdehyde (MDA), and levels of 8-iso Prostaglandin F2α (8-isoP). We then evaluated the ability of LGM2605 to mitigate asbestos-induced oxidative stress by administering LGM2605 (50 µM) 4-h prior to asbestos exposure. We observed a significant (p < 0.0001), time-dependent increase in asbestos-induced cytotoxicity, ROS generation, and the release of MDA and 8-iso Prostaglandin F2α, markers of lipid peroxidation, which increased linearly over time. LGM2605 treatment significantly (p < 0.0001) reduced asbestos-induced cytotoxicity and ROS generation, while decreasing levels of MDA and 8-isoP by 71%–88% and 41%–73%, respectively. Importantly, exposure to asbestos fibers induced cell protective defenses, such as cellular Nrf2 activation and the expression of phase II antioxidant enzymes, HO-1 and Nqo1 that were further enhanced by LGM2605 treatment. LGM2605 boosted antioxidant defenses, as well as reduced asbestos-induced ROS generation and markers of oxidative stress in murine peritoneal macrophages, supporting its possible use as a chemoprevention agent in the development of asbestos-induced malignant mesothelioma.

Downregulation of thymidylate synthase by RNAi molecules enhances the antitumor effect of pemetrexed in an orthotopic malignant mesothelioma xenograft mouse model

Malignant pleural mesothelioma (MPM) is an incurable cancer with an increasing incidence. Currently, pemetrexed (PMX)-based chemotherapy is the mainstay of chemotherapy for MPM, however, the outcome of PMX-based chemotherapy in patients with MPM is dismal. RNA interference (RNAi) technology has been considered as an effective tool to substantially enhance the therapeutic efficacy of chemotherapeutic agents in many preclinical and clinical settings. In this study, therefore, we investigated whether non-viral anti-thymidylate synthase RNAi embedded liposome (TS shRNA lipoplex) would effectively guide the downregulation of TS in human malignant mesothelioma MSTO-211H cells. Consequently, it enhanced the antitumor effect of PMX both in vitro and in vivo. TS shRNA effectively enhanced the in vitro cell growth inhibition upon treatment with PMX via downregulating TS expression in the MSTO-211H cell line. In in vivo orthotopic tumor model, the combined treatment of PMX and TS shRNA lipoplex efficiently combated the progression of orthotopic thoracic tumors and as a result prolonged mouse survival, compared to each single treatment. Our findings emphasize the pivotal relevance of RNAi as an effective tool for increasing the therapeutic efficacy of PMX, a cornerstone in the treatment regimens of MPM, and thereby, raising the possibility for the development of a novel therapeutic strategy, combination therapy of TS-shRNA and PMX, that can surpass many of the currently applied, but less effective, therapeutic regimens against lethal MPM.

Oncolytic virotherapy for human malignant mesothelioma: recent advances

Cancer virotherapy is an attractive alternative to conventional treatments because it offers a wide range of antitumor effects due to 1) the diversity of the oncolytic viruses that are now available and 2) their multifaceted activities against both tumor cells and tumor vessels, in addition to their ability to induce antitumor immune responses. In this review, we summarize preclinical and clinical data regarding the targeting of malignant mesothelioma (MM) by oncolytic viruses. We also discuss the potential of other oncolytic viruses that have already shown antitumor effects against several malignancies in advanced clinical trials but are yet to be tested against MM cells. Finally, we review how the activation of the immune system and combinations with other types of anticancer treatments could support the development of oncolytic virotherapy for the treatment of MM.

A clinical protocol to inhibit the HGF/c-Met pathway for malignant mesothelioma with an intrapleural injection of adenoviruses expressing the NK4 gene

Background

The hepatocyte growth factor (HGF)/c-Met signal pathway is up-regulated in human mesothelioma and suppression of the HGF/c-Met signaling with a competitive inhibitor, NK4 homologous to HGF in the structure, produced anti-tumor effects to mesothelioma in a preclinical study. Mesothelioma is highly resistant to a number of chemotherapeutic agents but distant metastasis to extra-thoracic organs is relatively infrequent until the late stage.

Methods/design

We planned to conduct a clinical study of gene therapy with adenoviruses expressing the NK4 gene (Ad-NK4) to control the local tumor growth. The study is designed to inject Ad-NK4 into the intrapleural cavity with a dose escalation manner from 10¹⁰ to 10¹² virus particles per patient and to examine safety and possible clinical benefits. The clinical investigation is a first-in-human trial to use the NK4 gene and to block the HGF/c-Met pathway with gene medicine. We conducted in vivo animal experiments to examine the safety level as one of the preclinical studies, and showed that Ad DNA administered in the pleural cavity was detected in many parenchymal organs. Biochemical and pathological analyses showed that liver damages were the major adverse effects with little toxicity to other organs. These studies firstly demonstrated biodistribution and transgene expression after an intrapleural injection of Ad vectors in an animal study, which contrasts with an intravenous injection showing relatively rapid clearance of Ad-NK4.

Discussion

The clinical study can also provide information regarding production of NK4 protein and antibody against NK4, and inhibition levels of the HGF/c-Met pathway by detecting dephosphorylation of c-Met in mesothelioma cells. These data will be crucial to judge whether local production of NK4 molecules can be an anti-cancer strategy.

Trial registration: UMIN clinical trials registry, Japan. Register ID: UMIN15771

Local and systemic therapies for malignant pleural mesothelioma

OPINION STATEMENT

Malignant pleural mesothelioma (MPM) is a challenging disease to treat with median overall survival times ranging between 9-17 months for all stages of disease. Recent clinical trials have improved our understanding of the biology of MPM. However, survival results are still not ideal. For early-stage MPM, patients should be evaluated for trimodality therapy in an experienced cancer center. If treating off-protocol, MPM patients should receive a surgical staging evaluation. The decision to proceed with surgical resection also should be considered after an extensive and thorough pulmonary and cardiac evaluation. If deemed a good surgical candidate, patients should receive surgical resection (pleurectomy/decortication or extrapleural pneumonectomy), adjuvant radiation therapy (hemithoracic external beam or intensity modulated radiation therapy), and either neoadjuvant or adjuvant chemotherapy (cisplatin-pemetrexed for 4 cycles). The optimal precise sequence of the trimodality is unclear and should be decided upon by a multidisciplinary consensus for each individual patient. In general, clinical trial participation should be encouraged. Several trials are currently underway to examine intraoperative therapies, vaccines, immunotherapy additions, and novel radiation therapy techniques. Advances in the field of MPM are reliant on participation in clinical trials and identifying biomarkers that are predictive for response to systemic therapies and prognostic for survival benefit.

Gene-mediated cytotoxic immunotherapy as adjuvant to surgery or chemoradiation for pancreatic adenocarcinoma

BACKGROUND

While surgical resection of pancreatic adenocarcinoma provides the only chance of cure, long-term survival remains poor. Immunotherapy may improve outcomes, especially as adjuvant to local therapies. Gene-mediated cytotoxic immunotherapy (GMCI) generates a systemic anti-tumor response through local delivery of an adenoviral vector expressing the HSV-tk gene (aglatimagene besadenovec, AdV-tk) followed by anti-herpetic prodrug. GMCI has demonstrated synergy with standard of care (SOC) in other tumor types. This is the first application in pancreatic cancer.

METHODS

Four dose levels (3 × 10(10) to 1 × 10(12) vector particles) were evaluated as adjuvant to surgery for resectable disease (Arm A) or to 5-FU chemoradiation for locally advanced disease (Arm B). Each patient received two cycles of AdV-tk + prodrug.

RESULTS

Twenty-four patients completed therapy, 12 per arm, with no dose-limiting toxicities. All Arm A patients were explored, eight were resected, one was locally advanced and three had distant metastases. CD8(+) T cell infiltration increased an average of 22-fold (range sixfold to 75-fold) compared with baseline (p = 0.0021). PD-L1 expression increased in 5/7 samples analyzed. One node-positive resected patient is alive >66 months without recurrence. Arm B RECIST response rate was 25 % with a median OS of 12 months and 1-year survival of 50 %. Patient-reported quality of life showed no evidence of deterioration.

CONCLUSIONS

AdV-tk can be safely combined with pancreatic cancer SOC without added toxicity. Response and survival compare favorably to expected outcomes and immune activity increased. These results support further evaluation of GMCI with more modern chemoradiation and surgery as well as PD-1/PD-L1 inhibitors in pancreatic cancer.

New and emerging therapeutic options for malignant pleural mesothelioma: review of early clinical trials

Malignant pleural mesothelioma (MPM) is a rare tumor that is challenging to control. Despite some benefit from using the multimodality-approach (surgery, combination chemotherapy and radiation), survival remains poor. However, current research produced a list of potential therapies. Here, we summarize significant new preclinical and early clinical developments in treatment of MPM, which include mesothelin specific antibody and toxin therapies, interleukin-4 (IL-4) receptor toxins, dendritic cell vaccines, immune checkpoint inhibitors, and gene-based therapies. In addition, several local modalities such as photodynamic therapy, postoperative lavage using betadine, and cryotherapy for local recurrence, have also shown to be effective for local control of disease.

Ask the Experts: Gene therapy in malignant pleural mesothelioma

Dr Masatoshi Tagawa graduated with MD from the School of Medicine, Chiba University (Chiba, Japan) and completed the graduated course in Chiba University (awarded PhD) in 1984. He spent a few years in Stanford University (CA, USA) as a postdoctoral fellow and became an assistant professor at Chiba University. He then moved to Chiba Cancer Center Research Institute (Chiba, Japan) as the Head in Division of Pathology and Cell Therapy, and became a professor of Graduate School of Medicine at Chiba University. He is currently a council member of the Japan Society of Gene Therapy and International Society of Cell and Gene Therapy of Cancer. He also serves as an editor of Cancer Gene Therapy. His primary research field is molecular biology and oncology and he is currently working on mesothelioma at preclinical and clinical research levels.

Novel therapeutic approaches for various cancer types using a modified sleeping beauty-based gene delivery system

Successful gene therapy largely depends on the selective introduction of therapeutic genes into the appropriate target cancer cells. One of the most effective and promising approaches for targeting tumor tissue during gene delivery is the use of viral vectors, which allow for high efficiency gene delivery. However, the use of viral vectors is not without risks and safety concerns, such as toxicities, a host immune response towards the viral antigens or potential viral recombination into the host's chromosome; these risks limit the clinical application of viral vectors. The Sleeping Beauty (SB) transposon-based system is an attractive, non-viral alternative to viral delivery systems. SB may be less immunogenic than the viral vector system due to its lack of viral sequences. The SB-based gene delivery system can stably integrate into the host cell genome to produce the therapeutic gene product over the lifetime of a cell. However, when compared to viral vectors, the non-viral SB-based gene delivery system still has limited therapeutic efficacy due to the lack of long-lasting gene expression potential and tumor cell specific gene transfer ability. These limitations could be overcome by modifying the SB system through the introduction of the hTERT promoter and the SV40 enhancer. In this study, a modified SB delivery system, under control of the hTERT promoter in conjunction with the SV40 enhancer, was able to successfully transfer the suicide gene (HSV-TK) into multiple types of cancer cells. The modified SB transfected cancer cells exhibited a significantly increased cancer cell specific death rate. These data suggest that our modified SB-based gene delivery system can be used as a safe and efficient tool for cancer cell specific therapeutic gene transfer and stable long-term expression.

Targeted expression of suicide gene by tissue-specific promoter and microRNA regulation for cancer gene therapy

In order to realise the full potential of cancer suicide gene therapy that allows the precise expression of suicide gene in cancer cells, we used a tissue specific Epithelial cell adhesion molecule (EpCAM) promoter (EGP-2) that directs transgene Herpes simplex virus–thymidine kinase (HSV-TK) expression preferentially in EpCAM over expressing cancer cells. EpCAM levels are considerably higher in retinoblastoma (RB), a childhood eye cancer with limited expression in normal cells. Use of miRNA regulation, adjacent to the use of the tissue-specific promoter, would provide the second layer of control to the transgene expression only in the tumor cells while sparing the normal cells. To test this hypothesis we cloned let-7b miRNA targets in the 3’UTR region of HSV-TK suicide gene driven by EpCAM promoter because let-7 family miRNAs, including let-7b, were found to be down regulated in the RB tumors and cell lines. We used EpCAM over expressing and let-7 down regulated RB cell lines Y79, WERI-Rb1 (EpCAM ^+ve/let-7b^{down-regulated}), EpCAM down regulated, let-7 over expressing normal retinal Müller glial cell line MIO-M1(EpCAM ^−ve/let-7b^up-regulated), and EpCAM up regulated, let-7b up-regulated normal thyroid cell line N-Thy-Ori-3.1(EpCAM ^+ve/let-7b^up-regulated) in the study. The cell proliferation was measured by MTT assay, apoptosis was measured by probing cleaved Caspase3, EpCAM and TK expression were quantified by Western blot. Our results showed that the EGP2-promoter HSV-TK (EGP2-TK) construct with 2 or 4 copies of let-7b miRNA targets expressed TK gene only in Y79, WERI-Rb-1, while the TK gene did not express in MIO-M1. In summary, we have developed a tissue-specific, miRNA-regulated dual control vector, which selectively expresses the suicide gene in EpCAM over expressing cells.

Highly efficient tumor transduction and antitumor efficacy in experimental human malignant mesothelioma using replicating gibbon ape leukemia virus

Retroviral replicating vectors (RRVs) have been shown to achieve efficient tumor transduction and enhanced therapeutic benefit in a wide variety of cancer models. Here we evaluated two different RRVs derived from amphotropic murine leukemia virus (AMLV) and gibbon ape leukemia virus (GALV), in human malignant mesothelioma cells. In vitro, both RRVs expressing the green fluorescent protein gene efficiently replicated in most mesothelioma cell lines tested, but not in normal mesothelial cells. Notably, in ACC-MESO-1 mesothelioma cells that were not permissive for AMLV-RRV, the GALV-RRV could spread efficiently in culture and in mice with subcutaneous xenografts by in vivo fluorescence imaging. Next, GALV-RRV expressing the cytosine deaminase prodrug activator gene showed efficient killing of ACC-MESO-1 cells in a prodrug 5-fluorocytosine dose-dependent manner, compared with AMLV-RRV. GALV-RRV-mediated prodrug activator gene therapy achieved significant inhibition of subcutaneous ACC-MESO-1 tumor growth in nude mice. Quantitative reverse transcription PCR demonstrated that ACC-MESO-1 cells express higher PiT-1 (GALV receptor) and lower PiT-2 (AMLV receptor) compared with normal mesothelial cells and other mesothelioma cells, presumably accounting for the distinctive finding that GALV-RRV replicates much more robustly than AMLV-RRV in these cells. These data indicate the potential utility of GALV-RRV-mediated prodrug activator gene therapy in the treatment of mesothelioma.

RGD capsid modification enhances mucosal protective immunity of a non-human primate adenovirus vector expressing Pseudomonas aeruginosa OprF

Replication-deficient adenoviral (Ad) vectors of non-human serotypes can serve as Ad vaccine platforms to circumvent pre-existing anti-human Ad immunity. We found previously that, in addition to that feature, a non-human primate-based AdC7 vector expressing outer membrane protein F of P. aeruginosa (AdC7OprF) was more potent in inducing lung mucosal and protective immunity compared to a human Ad5-based vector. In this study we analysed if genetic modification of the AdC7 fibre to display an integrin-binding arginine-glycine-aspartic acid (RGD) sequence can further enhance lung mucosal immunogenicity of AdC7OprF. Intratracheal immunization of mice with either AdC7OprF.RGD or AdC7OprF induced robust serum levels of anti-OprF immunoglobulin (Ig)G up to 12 weeks that were higher compared to immunization with the human vectors Ad5OprF or Ad5OprF.RGD. OprF-specific cellular responses in lung T cells isolated from mice immunized with AdC7OprF.RGD and AdC7OprF were similar for T helper type 1 (Th1) [interferon (IFN)-γ in CD8(+) and interleukin (IL)-12 in CD4(+)], Th2 (IL-4, IL-5 and IL-13 in CD4(+)) and Th17 (IL-17 in CD4(+)). Interestingly, AdC7OprF.RGD induced more robust protective immunity against pulmonary infection with P. aeruginosa compared to AdC7OprF or the control Ad5 vectors. The enhanced protective immunity induced by AdC7OprF.RGD was maintained in the absence of alveolar macrophages (AM) or CD1d natural killer T cells. Together, the data suggest that addition of RGD to the fibre of an AdC7-based vaccine is useful to enhance its mucosal protective immunogenicity.

E1B-55 kDa-defective adenoviruses activate p53 in mesothelioma and enhance cytotoxicity of anticancer agents

INTRODUCTION

Genetic characterization of malignant mesothelioma shows a homozygous deletion of the INK4A/ARF locus, which results in inactivation of the p53 pathways.

METHODS

We examined possible antitumor effects of adenoviruses with a deletion of the E1B-55kD gene (Ad-delE1B55) on mesothelioma and investigated combinatory actions with the first-line chemotherapeutic agents.

RESULTS

Ad-delE1B55 produced cytotoxicity on mesothelioma cells, which was associated with p53 phosphorylation, pRb dephosphorylation, and cleavage of caspases. Ad-delE1B55-infected cells displayed hyperploidy at the cell-cycle analysis and showed enlarged nuclear configurations. Combination of Ad-delE1B55 plus cisplatin or pemetrexed produced antitumor effects in vitro. Furthermore, Ad-delE1B55 and cisplatin showed combinatory effects in an orthotopic animal model.

CONCLUSIONS

Cell death caused by Ad-delE1B55 is attributable to cell-cycle arrest at M-phase checkpoint followed by activated apoptotic pathways, and combination of the first-line chemotherapeutic agents and the oncolytic adenovirus is a potential therapeutic for mesothelioma.

Systemically administered liposome-encapsulated Ad-PEDF potentiates the anti-cancer effects in mouse lung metastasis melanoma

BACKGROUND

The use of adenoviral vector for gene therapy is still an important strategy for advanced cancers, however, the lack of the requisite coxsackie-adenovirus receptor in cancer cells and host immune response to adenovirus limit the application of adenoviral vector in vivo.

METHOD

We designed the antiangiogenic gene therapy with recombinant PEDF adenovirus (Ad-PEDF) encapsulated in cationic liposome (Ad-PEDF/Liposome), and investigated the anti-tumor efficacy of Ad-PEDF/Liposome complex on inhibition of tumor metastasis.

RESULTS

We found that systemic administration of Ad-PEDF/liposome was well tolerated and resulted in marked suppression of tumor growth, and was more potent than uncoated Ad-PEDF to induce apoptosis in B16-F10 melanoma cells and inhibit murine pulmonary metastases in vivo. After Ad-luciferase was encapsulated with liposome, its distribution decreased in liver and increased in lung. The anti-Ad IgG level of Ad-PEDF/Liposome was significantly lower than Ad-PEDF used alone.

CONCLUSION

The present findings provide evidences of systematic administration of cationic liposome-encapsulated Ad-PEDF in pulmonary metastatic melanoma mice model, and show an encouraging therapeutic effect for further exploration and application of more complexes based on liposome-encapsulated adenovirus for more cancers.

Gene therapy for malignant mesothelioma: current prospects and challenges

Malignant mesothelioma, developed in the thoracic cavity, is resistant to current treatments. Suppression of the local tumor growth is beneficial to the patients since mesothelioma infrequently metastasizes to extrapleural organs. A majority of the tumors have a homologous genetic deletion at the INK4A/ARF locus that includes the p14ARF and the p16INK4A genes, and the genetic defect results in an inactivation of the p53-mediated pathways and in progression of cell cycle through pRb phosphorylation. Preclinical studies targeting the genetic abnormality with adenoviruses showed that restoration of the p53 pathways induced pRb dephosphorylation and subsequently produced anti-tumor effects. A number of preclinical studies with different genes and vector systems demonstrated the therapeutic efficacy and raised the possibility of gene therapy in clinical settings. An intrapleural administration of vectors has several advantages in transducing pleural mesothelioma but activates rapid antibody production which impedes further gene expression. There have been several clinical studies conducted for mesothelioma and these trials showed the feasibility of intrapleural administrations of adenovirus vectors. In this review we summarize major preclinical and clinical gene therapy for mesothelioma, and discuss the advantages of gene therapy in the context of stimulating host immune systems. Accumulating clinical data suggest that an intrapleural administration of viral vectors has distinct aspects which are not observed in other administration routes.

Malignant pleural mesothelioma: update on treatment options with a focus on novel therapies

There is evidence that improved treatments of malignant pleural mesothelioma are increasing the quality and quantity of life for patients with mesothelioma. Multimodality treatment programs that combine maximal surgical cytoreduction with novel forms of radiation therapy and more effective chemotherapy combinations may offer significant increases in survival for certain subgroups of patients with mesothelioma. Lung-sparing surgery may allow improvements in pulmonary function after surgery-based multimodality therapy, and potential longer overall survival than that seen with extrapleural pneumonectomy. Experimental treatments provide hope for all patients with mesothelioma, and in the future may be combined with standard therapy in multimodality protocols.

Cytoreduction surgery reduces systemic myeloid suppressor cell populations and restores intratumoral immunotherapy effectiveness

Background

Multiple immunotherapy approaches have improved adaptive anti-tumor immune responses in patients with early stage disease; however, results have been less dramatic when treating patients with late stage disease. These blunted responses are likely due to a host of factors, including changes in the tumor microenvironment and systemic immunosuppressive features, which accompany advanced tumor states. We hypothesized that cytoreductive surgery could control these immunosuppressive networks and restore the potency of immunotherapy in advanced disease scenarios.

Methods

To test these hypotheses, two representative intratumoral immunotherapies (an adenoviral vector encoding a suicide gene, AdV-tk, or a type-I interferon, Ad.IFNα) were tested in murine models of lung cancer. Cytoreductive surgery was performed following treatment of advanced tumors. Mechanistic underpinnings were investigated using flow cytometry, in vivo leukocyte depletion methods and in vivo tumor neutralization assays.

Results

AdV-tk and Ad.IFNα were effective in treating early lung cancers, but had little anti-tumor effects in late stage cancers. Interestingly, in late stage scenarios, surgical cytoreduction unmasked the anti-tumor potency of both immunotherapeutic approaches. Immune mechanisms that explained restoration in anti-tumor immune responses included increased CD8 T-cell trafficking and reduced myeloid derived suppressor cell populations.

Conclusion

This study demonstrates that surgical resection combined with immunotherapy may be a rational therapeutic option for patients with advanced stage cancer.

Upregulated p53 expression activates apoptotic pathways in wild-type p53-bearing mesothelioma and enhances cytotoxicity of cisplatin and pemetrexed

The majority of malignant mesothelioma possesses the wild-type p53 gene with a homologous deletion of the INK4A/ARF locus containing the p14(ARF) and the p16(INK4A) genes. We examined whether forced expression of p53 inhibited growth of mesothelioma cells and produced anti-tumor effects by a combination of cisplatin (CDDP) or pemetrexed (PEM), the first-line drugs for mesothelioma treatments. Transduction of mesothelioma cells with adenoviruses bearing the p53 gene (Ad-p53) induced phosphorylation of p53, upregulated Mdm2 and p21 expression levels and decreased phosphorylation of pRb. The transduction generated cleavage of caspase-8 and -3, but not caspase-9. Cell cycle analysis showed increased G0/G1- or G2/M-phase populations and subsequently sub-G1 fractions, depending on cell types and Ad-p53 doses. Transduction with Ad-p53 suppressed viability of mesothelioma cells and augmented the growth inhibition by CDDP or PEM mostly in a synergistic manner. Intrapleural injection of Ad-p53 and systemic administration of CDDP produced anti-tumor effects in an orthotopic animal model. These data collectively suggest that Ad-p53 is a possible agent for mesothelioma in combination with the first-line chemotherapeutics.

Gene therapy for lung neoplasms

Both advanced-stage lung cancer and malignant pleural mesothelioma are associated with a poor prognosis. Advances in treatment regimens for both diseases have had only a modest effect on their progressive course. Gene therapy for thoracic malignancies represents a novel therapeutic approach and has been evaluated in several clinical trials. Strategies have included induction of apoptosis, tumor suppressor gene replacement, suicide gene expression, cytokine-based therapy, various vaccination approaches, and adoptive transfer of modified immune cells. This review considers the clinical results, limitations, and future directions of gene therapy trials for thoracic malignancies.

Cytotoxic immunotherapy strategies for cancer: mechanisms and clinical development

Traditional therapies for cancer include surgery, chemotherapy, and radiation. Chemotherapy has widespread systemic cytotoxic effects against tumor cells but also affects normal cells. Radiation has more targeted local cytotoxicity but is limited to killing cells in the radiation field. Immunotherapy has the potential for systemic, specific killing of tumor cells. However, if the immune response is specific to a single antigen, tumor evasion can occur by down-regulation of that antigen. An immunotherapy approach that induces polyvalent immunity to autologous tumor antigens can provide a personalized vaccine with less potential for immunologic escape. A cytotoxic immunotherapy strategy creates such a tumor vaccine in situ. Immunogenic tumor cell death provides tumor antigen targets for the adaptive immune response and stimulates innate immunity. Attraction and activation of antigen presenting cells such as dendritic cells is important to process and present tumor antigens to T cells. These include cytotoxic T cells that kill tumor cells and T cells which positively and negatively regulate immunity. Tipping the balance in favor of anti-tumor immunity is an important aspect of an effective strategy. Clinically, immunotherapies may be most effective when combined with standard therapies in a complimentary way. An example is gene-mediated cytotoxic immunotherapy (GMCI) which uses an adenoviral vector, AdV-tk, to deliver a cytotoxic and immunostimulatory gene to tumor cells in vivo in combination with standard therapies creating an immunostimulatory milieu. This approach, studied extensively in animal models and early stage clinical trials, is now entering a definitive Phase 3 trial for prostate cancer.

Selective killing of lung cancer cells using carcinoembryonic antigen promoter and double suicide genes, thymidine kinase and cytosine deaminase (pCEA-TK/CD)

The application of gene therapy in cancer treatment is limited by non-specific targeting. In the present study, we constructed a recombinant plasmid, containing a carcinoembryonic antigen (CEA) promoter and double suicide genes thymidine kinase (TK) and cytosine deaminase (CD), henceforth referred to as pCEA-TK/CD. Our results showed that the CEA promoter can specifically drive target gene expression in CEA-positive lung cancer cells. In the presence of prodrugs 5-flucytosine and ganciclovir, pCEA-TK/CD transfection decreased inhibitory concentration 50 and increased apoptosis and cyclomorphosis. Our result suggests that gene therapy using pCEA-TK/CD may be a promising new approach for treating lung cancer.

Gene therapy for mesothelioma

Mesothelioma represents an especially good target for gene therapy since few effective therapies exist, the disease remained relatively localized until late in its course, the tumor can be accessed relatively easily through the chest wall, and the thin layer of mesothelial cells offers a large surface area for efficient, rapid, and diffuse gene transfer. Gene therapy trials in mesothelioma have shown safety, and some limited evidence of efficacy. We present a review of clinical trials that have been performed in mesothelioma and describe several new approaches currently being pursued.

Neoadjuvant in situ gene-mediated cytotoxic immunotherapy improves postoperative outcomes in novel syngeneic esophageal carcinoma models

Esophageal carcinoma is the most rapidly increasing tumor in the United States and has a dismal 15% 5-year survival. Immunotherapy has been proposed to improve patient outcomes; however, no immunocompetent esophageal carcinoma model exists to date to test this approach. We developed two mouse models of esophageal cancer by inoculating immunocompetent mice with syngeneic esophageal cell lines transformed by cyclin-D1 or mutant HRAS^G12V and loss of p53. Similar to humans, surgery and adjuvant chemotherapy (cisplatin and 5-fluorouracil) demonstrated limited efficacy. Gene-mediated cyototoxic immunotherapy (adenoviral vector carrying the herpes simplex virus thymidine kinase gene in combination with the prodrug ganciclovir; AdV-tk/GCV) demonstrated high levels of in vitro transduction and efficacy. Using in vivo syngeneic esophageal carcinoma models, combining surgery, chemotherapy and AdV-tk/GCV improved survival (P=0.007) and decreased disease recurrence (P<0.001). Mechanistic studies suggested that AdV-tk/GCV mediated a direct cytotoxic effect and an increased intra-tumoral trafficking of CD8 T cells (8.15% vs 14.89%, P=0.02). These data provide the first preclinical evidence that augmenting standard of care with immunotherapy may improve outcomes in the management of esophageal carcinoma.

Investigational approaches for mesothelioma

Malignant pleural mesothelioma (MPM) is a rare, aggressive tumor with a poor prognosis. In view of the poor survival benefit from first-line chemotherapy and the lack of subsequent effective treatment options, there is a strong need for the development of more effective treatment approaches for patients with MPM. This review will provide a comprehensive state of the art of new investigational approaches for mesothelioma. In an introductory section, the etiology, epidemiology, natural history, and standard of care treatment for MPM will be discussed. This review provide an update of the major clinical trials that impact mesothelioma treatment, discuss the impact of novel therapeutics, and provide perspective on where the clinical research in mesothelioma is moving. The evidence was collected by a systematic analysis of the literature (2000-2011) using the databases Medline (National Library of Medicine, USA), Embase (Elsevier, Netherlands), Cochrane Library (Great Britain), National Guideline Clearinghouse (USA), HTA Database (International Network of Agencies for Health Technology Assessment - INAHTA), NIH database (USA), International Pleural Mesothelioma Program - WHOLIS (WHO Database), with the following keywords and filters: mesothelioma, guidelines, treatment, surgery, chemotherapy, radiotherapy, review, investigational, drugs. Currently different targeted therapies and biologicals are under investigation for MPM. It is important that the molecular biologic research should first focus on mesothelioma-specific pathways and biomarkers in order to have more effective treatment options for this disease. The use of array technology will be certainly an implicit gain in the identification of new potential prognostic or biomarkers or important pathways in the MPM pathogenesis. Probably a central mesothelioma virtual tissue bank may contribute to the ultimate goal to identify druggable targets and to develop personalized treatment for the MPM patients.

Phase IB study of gene-mediated cytotoxic immunotherapy adjuvant to up-front surgery and intensive timing radiation for malignant glioma

PURPOSE

Despite aggressive therapies, median survival for malignant gliomas is less than 15 months. Patients with unmethylated O(6)-methylguanine-DNA methyltransferase (MGMT) fare worse, presumably because of temozolomide resistance. AdV-tk, an adenoviral vector containing the herpes simplex virus thymidine kinase gene, plus prodrug synergizes with surgery and chemoradiotherapy, kills tumor cells, has not shown MGMT dependency, and elicits an antitumor vaccine effect.

PATIENTS AND METHODS

Patients with newly diagnosed malignant glioma received AdV-tk at 3 × 10(10), 1 × 10(11), or 3 × 10(11) vector particles (vp) via tumor bed injection at time of surgery followed by 14 days of valacyclovir. Radiation was initiated within 9 days after AdV-tk injection to overlap with AdV-tk activity. Temozolomide was administered after completing valacyclovir treatment.

RESULTS

Accrual began December 2005 and was completed in 13 months. Thirteen patients were enrolled and 12 completed therapy, three at dose levels 1 and 2 and six at dose level 3. There were no dose-limiting or significant added toxicities. One patient withdrew before completing prodrug because of an unrelated surgical complication. Survival at 2 years was 33% and at 3 years was 25%. Patient-reported quality of life assessed with the Functional Assessment of Cancer Therapy-Brain (FACT-Br) was stable or improved after treatment. A significant CD3(+) T-cell infiltrate was found in four of four tumors analyzed after treatment. Three patients with MGMT unmethylated glioblastoma multiforme survived 6.5, 8.7, and 46.4 months.

CONCLUSION

AdV-tk plus valacyclovir can be safely delivered with surgery and accelerated radiation in newly diagnosed malignant gliomas. Temozolomide did not prevent immune responses. Although not powered for efficacy, the survival and MGMT independence trends are encouraging. A phase II trial is ongoing.

Replication-competent retrovirus vector-mediated prodrug activator gene therapy in experimental models of human malignant mesothelioma

Replication-competent retrovirus (RCR) vectors have been shown to achieve significantly enhanced tumor transduction efficiency and therapeutic efficacy in various cancer models. In the present study, we investigated RCR vector-mediated prodrug activator gene therapy for the treatment of malignant mesothelioma, a highly aggressive tumor with poor prognosis. RCR-GFP vector expressing the green fluorescent protein marker gene successfully infected and efficiently replicated in human malignant mesothelioma cell lines, as compared with non-malignant mesothelial cells in vitro. In mice with pre-established subcutaneous tumor xenografts, RCR-GFP vector showed robust spread throughout entire tumor masses after intratumoral administration. Next, RCR-cytosine deaminase (RCR-CD), expressing the yeast CD prodrug activator gene, showed efficient transmission of the prodrug activator gene associated with replicative spread of the virus, resulting in efficient killing of malignant mesothelioma cells in a prodrug 5-fluorocytosine (5FC)-dose dependent manner in vitro. After a single intratumoral injection of RCR-CD followed by intraperitoneal administration of 5FC, RCR vector-mediated prodrug activator gene therapy achieved significant inhibition of subcutaneous tumor growth, and significantly prolonged survival in the disseminated peritoneal model of malignant mesothelioma. These data indicate the potential utility of RCR vector-mediated prodrug activator gene therapy in the treatment of malignant mesothelioma.