A novel tumor-specific replication-restricted adenoviral vector for gene therapy of hepatocellular carcinoma

Expression of SIRPα-Fc by oncolytic virus enhances antitumor efficacy through tumor microenvironment reprogramming

Oncolytic viruses (OVs) selectively replicate within tumors, directly killing cancer cells and promoting a systemic immune response by releasing tumor antigens. These features make OVs a promising approach in tumor immunotherapy, offering targeted treatment with fewer side effects. Despite these advantages, OVs are primarily administered via intratumoral injection, limiting their effectiveness for advanced, systemic cancers. Among OVs, oncolytic adenoviruses (oAdVs) are the most widely studied due to their well-understood gene regulation, safety, and stability. In this study, a modified oAdV vector, pDC316-oAd-SA, was engineered to express the SIRPα-mIgG1Fc gene, designed to remodel tumor-associated macrophages (TAMs) and enhance anti-tumor immunity. This vector, along with a control virus (Ad-ON), was evaluated both in vitro and in vivo. The modified oAd-SA significantly improved macrophage phagocytosis and showed superior tumor regression in murine models. Additionally, while both oAdVs increased T cell infiltration in the tumor microenvironment, oAd-SA specifically enhanced T cell immune function. The study also revealed that oAdVs modulate TAMs differently across tumor types, with oAd-SA therapy particularly increasing TAM phagocytosis and promoting an anti-tumor response.

Role of homologous recombination/recombineering on human adenovirus genome engineering: Not the only but the most competent solution

Adenoviruses typically cause mild illnesses, but severe diseases may occur primarily in immunodeficient individuals, particularly children. Recently, adenoviruses have garnered significant interest as a versatile tool in gene therapy, tumor treatment, and vaccine vector development. Over the past two decades, the advent of recombineering, a method based on homologous recombination, has notably enhanced the utility of adenoviral vectors in therapeutic applications. This review summarizes recent advancements in the use of human adenoviral vectors in medicine and discusses the pivotal role of recombineering in the development of these vectors. Additionally, it highlights the current achievements and potential future impact of therapeutic adenoviral vectors.

High throughput screen for the improvement of inducible promoters for tumor microenvironment cues

Cancer immunotherapies are highly potent and are gaining wide clinical usage. However, severe side effects require focusing effector immune cell activities on the tumor microenvironment (TME). We recently developed a chimeric antigen receptor tumor-induced vector (CARTIV), a synthetic promoter activated by TME factors. To improve CARTIV functions including background, activation levels, and synergism, we screened a library of promoters with variations in key positions. Here, we present a screening method involving turning ON/OFF stimulating TNFα and IFNγ cytokines, followed by sequential cell sorting. Sequencing of enriched promoters identified seventeen candidates, which were cloned and whose activities were then validated, leading to the identification of two CARTIVs with lower background and higher induction. We further combined a third hypoxia element with the two-factor CARTIV, demonstrating additional modular improvement. Our study presents a method of fine-tuning synthetic promoters for desired immunotherapy needs.

Adenovirus Biology, Recombinant Adenovirus, and Adenovirus Usage in Gene Therapy

Gene therapy is currently in the public spotlight. Several gene therapy products, including oncolytic virus (OV), which predominantly replicates in and kills cancer cells, and COVID-19 vaccines have recently been commercialized. Recombinant adenoviruses, including replication-defective adenoviral vector and conditionally replicating adenovirus (CRA; oncolytic adenovirus), have been extensively studied and used in clinical trials for cancer and vaccines. Here, we review the biology of wild-type adenoviruses, the methodological principle for constructing recombinant adenoviruses, therapeutic applications of recombinant adenoviruses, and new technologies in pluripotent stem cell (PSC)-based regenerative medicine. Moreover, this article describes the technology platform for efficient construction of diverse "CRAs that can specifically target tumors with multiple factors" (m-CRAs). This technology allows for modification of four parts in the adenoviral E1 region and the subsequent insertion of a therapeutic gene and promoter to enhance cancer-specific viral replication (i.e., safety) as well as therapeutic effects. The screening study using the m-CRA technology successfully identified survivin-responsive m-CRA (Surv.m-CRA) as among the best m-CRAs, and clinical trials of Surv.m-CRA are underway for patients with cancer. This article also describes new recombinant adenovirus-based technologies for solving issues in PSC-based regenerative medicine.

Concepts in Oncolytic Adenovirus Therapy

Oncolytic adenovirus therapy is gaining importance as a novel treatment option for the management of various cancers. Different concepts of modification within the adenovirus vector have been identified that define the mode of action against and the interaction with the tumour. Adenoviral vectors allow for genetic manipulations that restrict tumour specificity and also the expression of specific transgenes in order to support the anti-tumour effect. Additionally, replication of the virus and reinfection of neighbouring tumour cells amplify the therapeutic effect. Another important aspect in oncolytic adenovirus therapy is the virus induced cell death which is a process that activates the immune system against the tumour. This review describes which elements in adenovirus vectors have been identified for modification not only to utilize oncolytic adenovirus vectors into conditionally replicating adenoviruses (CRAds) that allow replication specifically in tumour cells but also to confer specific characteristics to these viruses. These advances in development resulted in clinical trials that are summarized based on the conceptual design.

Inhibition of glioma by adenovirus KGHV500 encoding anti-p21Ras scFv and carried by cytokine-induced killer cells

Ras gene mutation or overexpression can lead to tumorigenesis in multiple kinds of cancer, including glioma. However, no drugs targeting Ras or its expression products have been approved for clinical application thus far. Adenoviral gene therapy is a promising method for the treatment of glioma. In this study, the human glioma cell line U251 was co-cultured with recombinant adenovirus KGHV500, and the anti-tumor effects of KGHV500 were determined by MTT, scratch test, Transwell invasion, and apoptosis assays. Then, KGHV500 was delivered via the intravenous injection of CIK cells into glioma xenografts. Tumor volume, ki67 proliferation index, apoptosis levels, and anti-p21Ras scFv expression were tested to evaluate targeting ability, anti-tumor efficacy, and safety. We found that the KGHV500 exhibited anti-tumor activity in U251 cells and increased the intracellular expression of anti-p21Ras scFv compared with that in the control groups. CIK cells delivered KGHV500 to U251 glioma cell xenografts and enhanced anti-tumor activity against glioma xenografts compared to that produced by the control treatment. In conclusion, targeting Ras is a useful therapeutic strategy for gliomas and other Ras-driven cancers, and the delivery of anti-p21Ras scFv by recombinant adenovirus and CIK cells may play an essential role in the therapy of Ras-driven cancers.

Oncolytic Adenovirus in Cancer Immunotherapy

Tumor-selective replicating "oncolytic" viruses are novel and promising tools for immunotherapy of cancer. However, despite their first success in clinical trials, previous experience suggests that currently used oncolytic virus monotherapies will not be effective enough to achieve complete tumor responses and long-term cure in a broad spectrum of cancers. Nevertheless, there are reasonable arguments that suggest advanced oncolytic viruses will play an essential role as enablers of multi-stage immunotherapies including established systemic immunotherapies. Oncolytic adenoviruses (oAds) display several features to meet this therapeutic need. oAds potently lyse infected tumor cells and induce a strong immunogenic cell death associated with tumor inflammation and induction of antitumor immune responses. Furthermore, established and versatile platforms of oAds exist, which are well suited for the incorporation of heterologous genes to optimally exploit and amplify the immunostimulatory effect of viral oncolysis. A considerable spectrum of functional genes has already been integrated in oAds to optimize particular aspects of immune stimulation including antigen presentation, T cell priming, engagement of additional effector functions, and interference with immunosuppression. These advanced concepts have the potential to play a promising future role as enablers of multi-stage immunotherapies involving adoptive cell transfer and systemic immunotherapies.

Cancer-Targeting Nanoparticles for Combinatorial Nucleic Acid Delivery

Nucleic acids are a promising type of therapeutic for the treatment of a wide range of conditions, including cancer, but they also pose many delivery challenges. For efficient and safe delivery to cancer cells, nucleic acids must generally be packaged into a vehicle, such as a nanoparticle, that will allow them to be taken up by the target cells and then released in the appropriate cellular compartment to function. As with other types of therapeutics, delivery vehicles for nucleic acids must also be designed to avoid unwanted side effects; thus, the ability of such carriers to target their cargo to cancer cells is crucial. Classes of nucleic acids, hurdles that must be overcome for effective intracellular delivery, types of nonviral nanomaterials used as delivery vehicles, and the different strategies that can be employed to target nucleic acid delivery specifically to tumor cells are discussed. Additonally, nanoparticle designs that facilitate multiplexed delivery of combinations of nucleic acids are reviewed.

Advances in delivery vectors for gene therapy in liver cancer

Hepatocellular carcinoma (HCC) is the third most common cause of cancer death globally, mainly due to lack of effective treatments – a problem that gene therapy is poised to solve. Successful gene therapy requires safe and efficient delivery vectors, and recent advances in both viral and nonviral vectors have made an important impact on HCC gene therapy delivery. This review explores how adenoviral, retroviral and adeno-associated viral vectors have been modified to increase safety and delivery capacity, highlighting studies and clinical trials using these vectors for HCC gene therapy. Nanoparticles, liposomes, exosomes and virosomes are also featured in their roles as HCC gene delivery vectors. Finally, new discoveries in gene editing technology and their impacts on HCC gene therapy are discussed.

The Development of Oncolytic Adenovirus Therapy in the Past and Future - For the Case of Pancreatic Cancer

Pancreatic cancer is an aggressive malignant disease and the efficacy of current treatments for unresectable diseases is quite limited despite recent advances. Gene therapy /virotherapy strategies may provide new options for the treatment of various cancers including pancreatic cancer. Oncolytic adenovirus shows an antitumoral effect via its intratumoral amplification and strong cytocidal effect in a variety of cancers and it has been employed for the development of potent oncolytic virotherapy agents for pancreatic cancer. Our ultimate goal is to develop an oncolytic adenovirus enabling the treatment of patients with advanced or spread diseases by systemic injection. Systemic application of oncolytic therapy mandates more efficient and selective gene delivery and needs to embody sufficient antitumor effect even with limited initial delivery to the tumor location. In this review, the current status of oncolytic adenoviruses from the viewpoints of vector design and potential strategies to overcome current obstacles for its clinical application will be described. We will also discuss the efforts to improve the antitumor activity of oncolytic adenovirus, in in vivo animal models, and the combination therapy of oncolytic adenovirus with radiation and chemotherapy.

Prostate Cancer-Specific of DD3-driven Oncolytic Virus-harboring mK5 Gene

Prostate cancer (PCa) is the second most diagnosed cancer in Western male population. In this study, we insert mK5 (the mutational kringle5 of human plasminogen) into a DD3-promoted (differential display code 3) oncolytic adenovirus to construct OncoAd.mK5.DD3. E1A.dE1B, briefly, O^Ad.DD3.mK5. DD3 is one of the most prostate cancer specific promoters which can transcriptionally control adenoviral replication. mK5 has been proved to be able to inhibit the tumor angiogenesis and inhibit cell proliferation. Our results suggested that targeting PCa with O^Ad.DD3.mK5 elicited strong antitumor effect.

Role of Gene Therapy in Pancreatic Cancer-A Review

Mortality from pancreatic ductal adenocarcinoma (PDAC) has remained essentially unchanged for decades and its relative contribution to overall cancer death is projected to only increase in the coming years. Current treatment for PDAC includes aggressive chemotherapy and surgical resection in a limited number of patients, with median survival of optimal treatment rather dismal. Recent advances in gene therapies offer novel opportunities for treatment, even in those with locally advanced disease. In this review, we summarize emerging techniques to the design and administration of virotherapy, synthetic vectors, and gene-editing technology. Despite these promising advances, shortcomings continue to exist and here will also be highlighted those approaches to overcoming obstacles in current laboratory and clinical research.

Hepatocellular carcinoma-targeting oncolytic adenovirus overcomes hypoxic tumor microenvironment and effectively disperses through both central and peripheral tumor regions

Cancer-specific promoter driven replication of oncolytic adenovirus (Ad) is cancer-specific, but shows low transcriptional activity. Thus, we generated several chimeric α-fetoprotein (AFP) promoter variants, containing reconstituted enhancer and silencer regions, to preferentially drive Ad replication in hepatocellular carcinoma (HCC). Modified AFP promoter, containing 2 enhancer A regions and a single enhancer B region (a2bm), showed strong and HCC-specific transcription. In AFP-positive HCCs, gene expression was 43- to 456-fold higher than those of control AFP promoter lacking enhancers. a2bm promoter was further modified by inserting multiple hypoxia-responsive elements (HRE) to generate Ha2bm promoter, which showed stronger transcriptional activity than a2bm promoter under hypoxic conditions. Ha2bm promoter-regulated oncolytic Ad (Ha2bm-d19) showed a stronger antitumor and proapoptotic effect than did a2bm promoter-regulated oncolytic Ad (a2bm-d19) in HCC xenograft tumors. Systemically administered Ha2bm-d19 caused no observable hepatotoxicity, whereas control replication-competent Ad, lacking cancer specificity (d19), induced significant hepatic damage. Ha2bm-d19 caused significantly lower expression of interleukin-6 than d19, showing that HCC-targeted delivery of Ad attenuates induction of the innate immune response against Ad. This chimeric AFP promoter enabled Ad to overcome the hypoxic tumor microenvironment and target HCC with high specificity, rendering it a promising candidate for the treatment of aggressive HCCs.

Oncolytic virus delivery: from nano-pharmacodynamics to enhanced oncolytic effect

With the advancement of a growing number of oncolytic viruses (OVs) to clinical development, drug delivery is becoming an important barrier to overcome for optimal therapeutic benefits. Host immunity, tumor microenvironment and abnormal vascularity contribute to inefficient vector delivery. A number of novel approaches for enhanced OV delivery are under evaluation, including use of nanoparticles, immunomodulatory agents and complex viral–particle ligands along with manipulations of the tumor microenvironment. This field of OV delivery has quickly evolved to bioengineering of complex nanoparticles that could be deposited within the tumor using minimal invasive image-guided delivery. Some of the strategies include ultrasound (US)-mediated cavitation-enhanced extravasation, magnetic viral complexes delivery, image-guided infusions with focused US and targeting photodynamic virotherapy. In addition, strategies that modulate tumor microenvironment to decrease extracellular matrix deposition and increase viral propagation are being used to improve tumor penetration by OVs. Some involve modification of the viral genome to enhance their tumoral penetration potential. Here, we highlight the barriers to oncolytic viral delivery, and discuss the challenges to improving it and the perspectives of establishing new modes of active delivery to achieve enhanced oncolytic effects.

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.

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.

Evolving lessons on nanomaterial-coated viral vectors for local and systemic gene therapy

Viral vectors are promising gene carriers for cancer therapy. However, virus-mediated gene therapies have demonstrated insufficient therapeutic efficacy in clinical trials due to rapid dissemination to nontarget tissues and to the immunogenicity of viral vectors, resulting in poor retention at the disease locus and induction of adverse inflammatory responses in patients. Further, the limited tropism of viral vectors prevents efficient gene delivery to target tissues. In this regard, modification of the viral surface with nanomaterials is a promising strategy to augment vector accumulation at the target tissue, circumvent the host immune response, and avoid nonspecific interactions with the reticuloendothelial system or serum complement. In the present review, we discuss various chemical modification strategies to enhance the therapeutic efficacy of viral vectors delivered either locally or systemically. We conclude by highlighting the salient features of various nanomaterial-coated viral vectors and their prospects and directions for future research.

Gene Therapies for Cancer: Strategies, Challenges and Successes

Gene therapy, which involves replacement of a defective gene with a functional, healthy copy of that gene, is a potentially beneficial cancer treatment approach particularly over chemotherapy, which often lacks selectivity and can cause non-specific toxicity. Despite significant progress pre-clinically with respect to both enhanced targeting and expression in a tumor-selective manner several hurdles still prevent success in the clinic, including non-specific expression, low-efficiency delivery and biosafety. Various innovative genetic approaches are under development to reconstruct vectors/transgenes to make them safer and more effective. Utilizing cutting-edge delivery technologies, gene expression can now be targeted in a tissue- and organ-specific manner. With these advances, gene therapy is poised to become amenable for routine cancer therapy with potential to elevate this methodology as a first line therapy for neoplastic diseases. This review discusses recent advances in gene therapy and their impact on a pre-clinical and clinical level.

Combination of bladder cancer-specific oncolytic adenovirus gene therapy with cisplatin on bladder cancer in vitro

Bladder cancer-specific oncolytic adenovirus Ad/PSCAE/UPII/E1A, carrying E1A gene regulated by human Uroplakin II (UPII) promoter and prostate stem cell antigen enhancer (PSCAE), could kill bladder tumor cells preferentially. The aim of this study was to examine the effects of Ad/PSCAE/UPII/E1A combined with cisplatin on human bladder cancer cells and to identify the underlying mechanisms. The combined effects of Ad/PSCAE/UPII/E1A and cisplatin on EJ, 5637, and BIU-87 bladder cancer cells were evaluated by MTT cell proliferation assay. Cell apoptosis was detected by flow cytometry with fluorescein isothiocyanate-conjugated annexin V (annexin V-FITC) and propidium iodide staining. The activation of the caspase pathway and the expression of Bcl-2 family proteins were determined by western blot assay. Ad/PSCAE/UPII/E1A adenovirus vector could infect bladder cancer cell lines selectively and induce growth inhibition effectively. Of note, the combination treatment of cisplatin and Ad/PSCAE/UPII/E1A could inhibit the proliferation of bladder cancer cells significantly compared with the "alone" treatment. Furthermore, Ad/PSCAE/UPII/E1A plus cisplatin combined treatment resulted in enhanced apoptosis in bladder cancer cells. The enhanced antitumor effects in vitro elicited by Ad/PSCAE/UPII/E1A plus cisplatin were closely related to the increased Fas expression and cleavage of caspase-8 and Bid and decrease in the ratio of anti- to pro-apoptotic proteins followed by activation of caspase-9 and caspase-3, which may contribute to the activation of extrinsic and intrinsic apoptotic pathways. Our results indicate that the combination of Ad/PSCAE/UPII/E1A with cisplatin exerts a synergistic antitumor effect on human bladder cancer cells and is a potential combined treatment strategy for bladder cancer.

Development of an immunotherapeutic adenovirus targeting hormone-independent prostate cancer

Background

To develop a targeting therapy for hormone-independent prostate cancer, we constructed and characterized conditionally replicating oncolytic adenovirus (Ad) equipped with mRFP (monomeric red fluorescence protein)/ttk (modified herpes simplex virus thymidine kinase). This construct was then further modified to express both mRFP/ttk and a soluble form of cytokine FLT3L (fms-related tyrosine kinase 3 ligand) simultaneously.

Methods

To construct the recombinant oncolytic adenovirus, E1a and E4 genes, which are necessary for adenovirus replication, were controlled by the prostate-specific enhancer sequence (PSES) targeting prostate cancer cells expressing prostate-specific antigen (PSA) and prostate-specific membrane antigen (PSMA). Simultaneously, it expressed the mRFP/ttk fusion protein in order to be able to elicit the cytotoxic effect.

Results

The Ad5/35PSES.mRFP/ttk chimeric recombinant adenovirus was generated successfully. When replication of Ad5/35PSES.mRFP/ttk was evaluated in prostate cancer cell lines under fluorescence microscopy, red fluorescence intensity increased more in LNCaP cells, suggesting that the mRFP/ttk fusion protein was folded functionally. In addition, the replication assay including wild-type adenovirus as a positive control showed that PSES-positive cells (LNCaP and CWR22rv) permitted virus replication but not PSES-negative cells (DU145 and PC3). Next, we evaluated the killing activity of this recombinant adenovirus. The Ad5/35PSES. mRFP/ttk killed LNCaP and CWR22rv more effectively. Unlike PSES-positive cells, DU145 and PC3 were resistant to killing by this recombinant adenovirus. Finally, in order to potentiate therapeutic efficacy, we developed a recombinant adenovirus expressing multiexogenous genes, mRFP/ttk and sFLT3L.

Conclusion

In the present study, a replication-competent adenovirus was successfully designed to replicate conditionally in PSA-positive and PSMA-positive prostate cancer cells. This recombinant adenovirus is equipped with the fusion protein of suicidal and red-fluorescence fusion protein together with sFLT3L. This construct would be expected to have potent antitumor effects and deserves more extensive investigation.

Combination of E2F-1 promoter-regulated oncolytic adenovirus and cytokine-induced killer cells enhances the antitumor effects in an orthotopic rectal cancer model

Due to the anatomical structure of the rectum, the treatment of rectal cancer remains challenging. Ad-E2F, an oncolytic adenovirus containing the E2F-1 promoter, can selectively replicate within and kill cancer cells derived from solid tumors. Thus, this virus provides a novel approach for the treatment of rectal cancer. Given the poor efficacy and possible adverse reactions that arise from the use of oncolytic virus alone and the results of our analysis of the efficacy of Ad-E2F in the treatment of rectal cancer, we investigated the use of oncolytic adenovirus in combination with adoptive immunotherapy using cytokine-induced killer (CIK) cells as a therapeutic treatment for rectal cancer. Our results illustrated that E2F-1 gene expression is higher in rectal cancer tissue than in normal tissue. Furthermore, the designed oncolytic adenovirus Ad-E2F is capable of selectively killing colorectal cell lines but has no significant effect on CIK cells. The results of in vitro and in vivo experiments demonstrated that combined therapy with Ad-E2F and CIK cells produce stronger antitumor effects than the administration of Ad-E2F or CIK cells alone. For low rectal cancers that are suitable for intratumoral injection, local injections of oncolytic viruses in combination with CIK cell-based adoptive immunotherapy may be suitable as a novel comprehensive therapeutic approach.

Meganuclease-mediated virus self-cleavage facilitates tumor-specific virus replication

Meganucleases can specifically cleave long DNA sequence motifs, a feature that makes them an ideal tool for gene engineering in living cells. In a proof-of-concept study, we investigated the use of the meganuclease I-Sce I for targeted virus self-disruption to generate high-specific oncolytic viruses. For this purpose, we provided oncolytic adenoviruses with a molecular circuit that selectively responds to p53 activation by expression of I-Sce I subsequently leading to self-disruption of the viral DNA via heterologous I-Sce I recognition sites within the virus genome. We observed that virus replication and cell lysis was effectively impaired in p53-normal cells, but not in p53-dysfunctional tumor cells. I-Sce I activity led to effective intracellular processing of viral DNA as confirmed by detection of specific cleavage products. Virus disruption did not interfere with E1A levels indicating that reduction of functional virus genomes was the predominant cause for conditional replication. Consequently, tumor-specific replication was further enhanced when E1A expression was additionally inhibited by targeted transcriptional repression. Finally, we demonstrated p53-dependent oncolysis by I-Sce I-expressing viruses in vitro and in vivo, and demonstrated effective inhibition of tumor growth. In summary, meganuclease-mediated virus cleavage represents a promising approach to provide oncolytic viruses with attractive safety profiles.

Tumor suppressor in lung cancer-1 (TSLC1) mediated by dual-regulated oncolytic adenovirus exerts specific antitumor actions in a mouse model

AIM

The tumor suppressor in lung cancer-1 (TSLC1) is a candidate tumor suppressor of lung cancer, and frequently inactivated in primary non-small cell lung cancer (NSCLC). In this study, we investigated the effects of TSLC1 mediated by a dual-regulated oncolytic adenovirus on lung cancer, and the mechanisms underlying the antitumor actions.

METHODS

The recombinant virus Ad·sp-E1A(Δ24)-TSLC1 was constructed by inserting the TSLC1 gene into the dual-regulated Ad·sp-E1A(Δ24) vector, which contained the survivin promoter and a 24 bp deletion within E1A. The antitumor effects of Ad·sp-E1A(Δ24)-TSLC1 were evaluated in NCI-H460, A549, and H1299 lung cancer cell lines and the normal fibroblast cell line MRC-5, as well as in A549 xenograft model in nude mice. Cell viability was assessed using MTT assay. The expression of TSLC1 and activation of the caspase signaling pathway were detected by Western blot analyses. The tumor tissues from the xenograft models were examined using H&E staining, IHC, TUNEL, and TEM analyses.

RESULTS

Infection of A549 lung cancer cells with Ad·sp-E1A(Δ24)-TSLC1 induced high level expression of TSLC1. Furthermore, the Ad·sp-E1A(Δ24)-TSLC1 virus dose-dependently suppressed the viability of NCI-H460, A549, and H1299 lung cancer cells, and did not affect MRC-5 normal fibroblast cells. Infection of NCI-H460, A549, and H1299 lung cancer cells with Ad·sp-E1A(Δ24)-TSLC1 induced apoptosis, and increased activation of caspase-8, caspase-3 and PARP. In A549 xenograft model in nude mice, intratumoral injection of Ad·sp-E1A(Δ24)-TSLC1 significantly suppressed the tumor volume, and increased the survival rate (from less than 15% to 87.5% at d 60). Histological studies showed that injection of Ad·sp-E1A(Δ24)-TSLC1 caused tumor cell apoptosis and virus particle propagation in tumor tissues.

CONCLUSION

The oncolytic adenovirus Ad·sp-E1A(Δ24)-TSLC1 exhibits specific antitumor effects, and is a promising agent for the treatment of lung cancer.

Chapter One---Cancer terminator viruses and approaches for enhancing therapeutic outcomes

No single or combinatorial therapeutic approach has proven effective in decreasing morbidity or engendering a cure of metastatic cancer. In principle, conditionally replication-competent adenoviruses that induce tumor oncolysis through cancer-specific replication hold promise for cancer therapy. However, a single-agent approach may not be adequate to completely eradicate cancer in a patient because most cancers arise from abnormalities in multiple genetic and signal transduction pathways and targeting disseminated metastases is difficult to achieve. Based on these considerations, a novel class of cancer destroying adenoviruses have been produced, cancer terminator viruses (CTVs), in which cancer-specific replication is controlled by the progression-elevated gene-3 promoter and replicating viruses produce a second transgene encoding an apoptosis-inducing and immunomodulatory cytokine, either melanoma differentiation-associated gene-7/interleukin-24 (mda-7/IL-24) or interferon-γ. This review focuses on these viruses and ways to improve their delivery systemically and enhance their therapeutic efficacy.

Exploiting the Intron-splicing Mechanism of Insect Cells to Produce Viral Vectors Harboring Toxic Genes for Suicide Gene Therapy

Two mammalian introns, the human growth hormone intron and the Simian virus 40 large T antigen intron, were inserted into the coding sequences of diphtheria toxin fragment A (DT-A) and barnase (Bar), respectively, to disrupt their open-reading frames (ORFs). Expression of these two toxic proteins were totally abolished, which enabled the production of normal levels of recombinant baculoviral and adeno-associated viral (AAV) vectors in insect cells. When these viral vectors were introduced into mammalian cells, the introns were spliced out and the toxic proteins were expressed, which resulted in apoptosis in mammalian cells. This is the first report to show that viral vectors harboring toxin genes can be produced at normal levels by exploiting the intron-splicing mechanism of insect cells. Furthermore, viral vectors carrying the DT-A gene under control of tumor-specific promoters were able to exert tumor-specific cell killing. This novel method to produce viral vectors harboring toxic genes under control of tumor-specific promoter offers a powerful tool for further research, as well as for the development of toxin-based suicide gene therapy drugs.Molecular Therapy - Nucleic Acids (2012) 1, e57; doi:10.1038/mtna.2012.48; published online 27 November 2012.

Infectivity-selective oncolytic adenovirus developed by high-throughput screening of adenovirus-formatted library

Adenovirus (Ad) is a potent gene-delivery vehicle and has frequently been used for designing oncolytic viruses. However, lack of selectivity on infection has hampered the achievement of sufficient in vivo efficiency. Here, we developed a novel oncolytic virus system, infectivity-selective oncolytic adenovirus (ISOAd), via direct high-throughput screening of a high-diversity targeting-ligand library in adenoviral format. Through our newly designed rescue virus system, the high-diversity Ad library carrying the random seven amino acid sequences ligand-library in the AB-loop of its fiber-knob region (5 × 10(9) diversity) was successfully generated. During the screening of this library with the cells expressing the target molecule (mesothelin, MSLN), the AB-loop sequence of the virus clones converged to one dominant sequence and a novel MSLN-targeting sequence was isolated. The virus with the isolated motif showed selective infectivity to MSLN-positive cells in vitro. In vivo, it exhibited a selective and potent antitumor effect resulted from the viral replication in MSLN-positive xenografts. The ISOAd is a novel class of oncolytic Ad, which has selectivity at the step of transduction. The selectivity at the stage of infection can open new perspectives in oncolytic Ad therapy for various diseases.

Effects of G250 promoter controlled conditionally replicative adenovirus expressing Ki67-siRNA on renal cancer cell

Replication-competent adenovirus (RCAd) has been used extensively in cancer gene therapy, and tumor-selection is critical for the use of replication-competent adenovirus. Here we investigated the anti-tumor characterization of oncolytic virus, whose E1A gene is under the control of a renal cell carcinoma specific promoter - the G250 promoter. The constructed oncolytic virus G250-Ki67 is armed with transgene of Ki67-siRNA, and G250-ZD55-Ki67 also with E1B-55 KD deleted. The tumor-specific expression of E1A and Ki67 was demonstrated by Western blot and immunohistochemistry staining, and the tumor-specific cytotoxicity was assessed by crystal violet staining and cell viability assays. The G250-Ki67 and G250-ZD55-Ki67 adenoviruses could express E1A protein in 786-O and OSRC cell lines but not in ACHN and HK-2 cell lines. The expression of Ki67 gene in 786-O and OSRC cell lines were suppressed by these adenoviruses. The cytotoxic effects induced by G250-ZD55-Ki67 and G250-Ki67 were more obvious on the 786-O cell lines than on the OSRC cell lines. Each group of adenoviruses could inhibit the proliferation of the 786-O cells and OSRC cells. However, the effects induced by G250-ZD55-Ki67 and G250-Ki67 on 786-O cells were stronger than on OSRC cells. Moreover, G250-ZD55-Ki67 had enhanced antitumor activities in these renal cancer cells compared with G250-Ki67. G250 promoter-derived CRAds carrying Ki67-siRNA could highly amplify and express Ki67-siRNA in renal cancer cells with expression of G250 antigen, inhibit renal cancer cells proliferation and induce apoptosis. These results demonstrated that the G250-specific oncolytic adenovirus expressing Ki67-siRNA is applicable for human renal clear cell cancer therapy.

Complete eradication of hepatomas using an oncolytic adenovirus containing AFP promoter controlling E1A and an E1B deletion to drive IL-24 expression

Interleukin (IL)-24, a promising therapeutic gene, has been widely used for Cancer Targeting Gene-Viro-Therapy (CTGVT). In this study, IL-24 was inserted into an oncolytic adenovirus in which the E1A gene is driven by an enhanced, short α-fetoprotein (AFP) promoter and the E1B gene is completely deleted to form Ad.enAFP-E1A-ΔE1B-IL-24. This construct has a potent antitumor effect on liver cancer cell lines in vitro, but little or no effect on normal cell lines, such as L-02 and QSG-7701. In vivo, the complete elimination of Huh-7 liver cancer in nude mice with Ad.enAFP-E1A-ΔE1B-IL-24 intratumor injection was observed. The design of Ad.enAFP-E1A-ΔE1B-IL-24 and its potent antitumor effect on liver cancer have not been published previously. The mechanism of the potent antitumor effect of Ad.enAFP-E1A-ΔE1B-IL-24 is due to the upregulation of GADD34 and intrinsic and extrinsic apoptotic signaling.

Evolution of oncolytic adenovirus for cancer treatment

Oncolytic adenovirus (Ad) has been used in cancer gene therapy largely due to its ability to selectively infect and replicate in tumor cells. However, because the oncolytic antitumor activity is insufficient to effectively eliminate tumors, various strategies have been devised to improve the therapeutic efficacy. Single-vector Ads "armed" with short hairpin RNA, cytokines, or matrix-modulating proteins have been developed. Two clear advantages are viral amplification of the therapeutic gene, and the additive effects of oncolytic and therapeutic gene-mediated antitumor activities. To develop systemically injectable Ad carriers, strategies to modify the Ad surface with polymers, liposomes, or nanoparticles have been shown to extend circulation time, reduce immunogenicity, and result in increased antitumor effect as well as lower accumulation and toxicity in liver. Specific targeting platforms for tumor-selective oncolytic therapies against both primary and metastatic cancers have been developed. This review will focus on updated strategies to develop potent oncolytic Ads for use in cancer treatment.

Targeting Gene-Viro-Therapy with AFP driving Apoptin gene shows potent antitumor effect in hepatocarcinoma

Background

Gene therapy and viral therapy are used for cancer therapy for many years, but the results are less than satisfactory. Our aim was to construct a new recombinant adenovirus which is more efficient to kill hepatocarcinoma cells but more safe to normal cells.

Methods

By using the Cancer Targeting Gene-Viro-Therapy strategy, Apoptin, a promising cancer therapeutic gene was inserted into the double-regulated oncolytic adenovirus AD55 in which E1A gene was driven by alpha fetoprotein promoter along with a 55 kDa deletion in E1B gene to form AD55-Apoptin. The anti-tumor effects and safety were examined by western blotting, virus yield assay, real time polymerase chain reaction, 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay, Hoechst33342 staining, Fluorescence-activated cell sorting, xenograft tumor model, Immunohistochemical assay, liver function analysis and Terminal deoxynucleotidyl transferase mediated dUTP Nick End Labeling assay.

Results

The recombinant virus AD55-Apoptin has more significant antitumor effect for hepatocelluar carcinoma cell lines (in vitro) than that of AD55 and even ONYX-015 but no or little impair on normal cell lines. Furthermore, it also shows an obvious in vivo antitumor effect on the Huh-7 liver carcinoma xenograft in nude mice with bigger beginning tumor volume till about 425 mm3 but has no any damage on the function of liver. The induction of apoptosis is involved in AD55-Apoptin induced antitumor effects.

Conclusion

The AD55-Apoptin can be a potential anti-hepatoma agent with remarkable antitumor efficacy as well as higher safety in cancer targeting gene-viro-therapy system.

Inhibitory effect of Survivin promoter-regulated oncolytic adenovirus carrying P53 gene against gallbladder cancer

Gene therapy has become an important strategy for treatment of malignancies, but problems remains concerning the low gene transferring efficiency, poor transgene expression and limited targeting specific tumors, which have greatly hampered the clinical application of tumor gene therapy. Gallbladder cancer is characterized by rapid progress, poor prognosis, and aberrantly high expression of Survivin. In the present study, we used a human tumor-specific Survivin promoter-regulated oncolytic adenovirus vector carrying P53 gene, whose anti-cancer effect has been widely confirmed, to construct a wide spectrum, specific, safe, effective gene-viral therapy system, AdSurp-P53. Examining expression of enhanced green fluorecent protein (EGFP), E1A and the target gene P53 in the oncolytic adenovirus system validated that Survivin promoter-regulated oncolytic adenovirus had high proliferation activity and high P53 expression in Survivin-positive gallbladder cancer cells. Our in vitro cytotoxicity experiment demonstrated that AdSurp-P53 possessed a stronger cytotoxic effect against gallbladder cancer cells and hepatic cancer cells. The survival rate of EH-GB1 cells was lower than 40% after infection of AdSurp-P53 at multiplicity of infection (MOI) = 1 pfu/cell, while the rate was higher than 90% after infection of Ad-P53 at the same MOI, demonstrating that AdSurp-P53 has a potent cytotoxicity against EH-GB1 cells. The tumor growth was greatly inhibited in nude mice bearing EH-GB1 xenografts when the total dose of AdSurp-P53 was 1 × 10(9) pfu, and terminal dUTP nick end-labeling (TUNEL) revealed that the apoptotic rate of cancer cells was (33.4 ± 8.4)%. This oncolytic adenovirus system overcomes the long-standing shortcomings of gene therapy: poor transgene expression and targeting of only specific tumors, with its therapeutic effect better than the traditional Ad-P53 therapy regimen already on market; our system might be used for patients with advanced gallbladder cancer and other cancers, who are not sensitive to chemotherapy, radiotherapy, or who lost their chance for surgical treatment.

Current good manufacturing practice production of an oncolytic recombinant vesicular stomatitis viral vector for cancer treatment

Vesicular stomatitis virus (VSV) is an oncolytic virus currently being investigated as a promising tool to treat cancer because of its ability to selectively replicate in cancer cells. To enhance the oncolytic property of the nonpathologic laboratory strain of VSV, we generated a recombinant vector [rVSV(MΔ51)-M3] expressing murine gammaherpesvirus M3, a secreted viral chemokine-binding protein that binds to a broad range of mammalian chemokines with high affinity. As previously reported, when rVSV(MΔ51)-M3 was used in an orthotopic model of hepatocellular carcinoma (HCC) in rats, it suppressed inflammatory cell migration to the virus-infected tumor site, which allowed for enhanced intratumoral virus replication leading to increased tumor necrosis and substantially prolonged survival. These encouraging results led to the development of this vector for clinical translation in patients with HCC. However, a scalable current Good Manufacturing Practice (cGMP)-compliant manufacturing process has not been described for this vector. To produce the quantities of high-titer virus required for clinical trials, a process that is amenable to GMP manufacturing and scale-up was developed. We describe here a large-scale (50-liter) vector production process capable of achieving crude titers on the order of 10(9) plaque-forming units (PFU)/ml under cGMP. This process was used to generate a master virus seed stock and a clinical lot of the clinical trial agent under cGMP with an infectious viral titer of approximately 2 × 10(10) PFU/ml (total yield, 1 × 10(13) PFU). The lot has passed all U.S. Food and Drug Administration-mandated release testing and will be used in a phase 1 clinical translational trial in patients with advanced HCC.

The emerging role of viruses in the treatment of solid tumours

There is increasing optimism for the use of non-pathogenic viruses in the treatment of many cancers. Initial interest in oncolytic virotherapy was based on the observation of an occasional clinical resolution of a lymphoma after a systemic viral infection. In many cancers, by comparison with normal tissues, the competency of the cellular anti-viral mechanism is impaired, thus creating an exploitable difference between the tumour and normal cells, as an unimpeded viral proliferation in cancer cells is eventually cytocidal. In addition to their oncolytic capability, these particular viruses may be engineered to facilitate gene delivery to tumour cells to produce therapeutic effects such as cytokine secretion and anti -tumour immune responses prior to the eventual cytolysis. There is now promising clinical experience with these viral strategies, particularly as part of multimodal studies, and already several clinical trials are in progress. The limitations of standard cancer chemotherapies, including their lack of specificity with consequent collateral toxicity and the development of cross-resistance, do not appear to apply to viral-based therapies. Furthermore, virotherapy frequently restores chemoradiosensitivity to resistant tumours and has also demonstrated efficacy against cancers that historically have a dismal prognosis. While there is cause for optimism, through continued improvements in the efficiency and safety of systemic delivery, through the emergence of alternative viral agents and through favourable clinical experiences, clinical trials as part of multimodal protocols will be necessary to define clinical utility. Significant progress has been made and this is now a major research area with an increasing annual bibliography.

Cell cycle progression or translation control is not essential for vesicular stomatitis virus oncolysis of hepatocellular carcinoma

The intrinsic oncolytic specificity of vesicular stomatitis virus (VSV) is currently being exploited to develop alternative therapeutic strategies for hepatocellular carcinoma (HCC). Identifying key regulators in diverse transduction pathways that define VSV oncolysis in cancer cells represents a fundamental prerequisite to engineering more effective oncolytic viral vectors and adjusting combination therapies. After having identified defects in the signalling cascade of type I interferon induction, responsible for attenuated antiviral responses in human HCC cell lines, we have now investigated the role of cell proliferation and translation initiation. Cell cycle progression and translation initiation factors eIF4E and eIF2Bε have been recently identified as key regulators of VSV permissiveness in T-lymphocytes and immortalized mouse embryonic fibroblasts, respectively. Here, we show that in HCC, decrease of cell proliferation by cell cycle inhibitors or siRNA-mediated reduction of G(1) cyclin-dependent kinase activities (CDK4) or cyclin D1 protein expression, do not significantly alter viral growth. Additionally, we demonstrate that translation initiation factors eIF4E and eIF2Bε are negligible in sustaining VSV replication in HCC. Taken together, these results indicate that cellular proliferation and the initiation phase of cellular protein synthesis are not essential for successful VSV oncolysis of HCC. Moreover, our observations indicate the importance of cell-type specificity for VSV oncolysis, an important aspect to be considered in virotherapy applications in the future.

The development of the conditionally replication-competent adenovirus: replacement of E4 orf1-4 region by exogenous gene

BACKGROUND

Tumor or tissue specific replicative adenovirus armed with a therapeutic gene has shown a promising anti-cancer therapeutic modality. However, because the genomic packaging capacity is constrained, only a few places inside it are available for transgene insertion. In the present study, we introduce a novel strategy utilizing the early E4 region for the insertion of therapeutic gene(s).

METHODS

We constructed the conditionally replication-competent adenovirus (CRAd), Ad5E4(mRFP) by: (i) replacing the E4/E1a promoter by the prostate-specific enhancer element; (ii) inserting mRFP inside the E4orf1-4 deletion region; and (iii) sub-cloning enhanced green fluorescent protein controlled by cytomegalovirus promoter in the left end of the viral genome. Subsequently, we evaluated its replication abilities and killing activities in vitro, as well as its in vivo anti-tumor efficacy in CWR22rv xenografts.

RESULTS

When infected with Ad5E4(mRFP), the number and intensity of the mRFP gene products increased in a prostate cancer cell-specific manner as designed, suggesting that the mRFP gene and E4orfs other than E4orf1-4 were well synthesized from one transcript via alternative splicing as the recombinant adenovirus replicated. As expected from the confirmed virus replication capability, Ad5E4(mRFP) induced cell lysis as potent as the wild-type adenovirus and effectively suppressed tumor growth when tested in the CWR22rv xenografts in nude mice. Furthermore, Ad5E4(endo/angio) harboring an endostatin-angiostatin gene in E4orf1-4 was able to enhance CRAd by replacing mRFP with a therapeutic gene.

CONCLUSIONS

The approach employed in the present study for the insertion of a therapeutic transgene in CRAd should facilitate the construction of CRAd containing multiple therapeutic genes in the viral genome that may have the potential to serve as highly potent cancer therapeutic reagents.

Oncolytic (replication-competent) adenoviruses as anticancer agents

IMPORTANCE OF THE FIELD

Whilst therapies for neoplasies have advanced tremendously in the last few decades, there is still a need for new anti-cancer treatments. One option is genetically-engineered oncolytic adenovirus (Ad) 'vectors'. These kill cancer cells via the viral replication cycle, and amplify the anti-tumor effect by producing progeny virions able to infect neighboring tumor cells.

AREAS COVERED IN THIS REVIEW

We provide a description of basic Ad biology and summarize the literature for oncolytic Ads from 1996 to the present.

WHAT THE READER WILL GAIN

An overall view of oncolytic Ads, the merits and drawbacks of the various features of these vectors, and obstacles to further development and future directions for research.

TAKE HOME MESSAGE

Ads are attractive for gene therapy because they are relatively innocuous, easy to produce in large quantities, genetically stable, and easy to manipulate. A variety of have been constructed and tested, in pre-clinical and clinical experiments. Oncolytic Ads proved to be remarkably safe; no dose-limiting toxicity was observed in any clinical trial, and the maximum tolerated dose was not reached. At present, the major challenge for researchers is to increase the efficacy of the vectors, and to incorporate oncolytic virotherapy into existing treatment protocols.

Evaluation of biodistribution of a fiber-chimeric, conditionally replication-competent (oncolytic) adenovirus in CD46 receptor transgenic mice

The limited efficacy of adenovirus type 5 (Ad5)-based oncolytic viruses seen in the clinic thus far may be attributable in part to variable expression of its receptor on tumor cells. Replacement of the Ad5 fiber knob with the Ad35 fiber knob generated the Ad5/35 chimeric virus, which has previously been demonstrated to have significant antitumor activity in murine tumor models, presumably by virtue of its recognition of the CD46 receptor, which is abundant on many types of tumor cells. In the current study, a CD46 receptor transgenic mouse strain (hCD46Ge) that expresses the CD46 receptor in a pattern closely mirroring that in humans was used to study the in vivo properties of Ad5/Ad35 chimeric viruses. Vector distribution was evaluated after intravenous administration to hCD46Ge mice of an Ad5-based oncolytic adenovirus or an Ad5/35 chimeric oncolytic adenovirus (designated OV-5 and OV-5T35H, respectively), a wild-type Ad5 virus (Ad5wt), or an Ad5-based, E1-deleted adenovirus (Addl312) at 1.25 x 10(12) viral particles/kg. The amount of OV-5T35H vector genomes in the liver was at least two orders of magnitude lower than that of Ad5-based viruses. Moreover, animals injected with OV-5T35H virus had significantly lower elevations of serum proinflammatory cytokines and liver enzyme levels. Mice injected with Ad5wt lost more than 20% of their body weight and died or required euthanasia because of poor clinical condition within 4 days of virus administration. Mice treated with OV-5 lost as much as 15% of their body weight over 8-9 days, but recovered within 14 days. Mice that were treated with Addl312 or OV-5T35H exhibited no body weight loss during the study period. These studies suggest that the Ad5/35-based chimeric viruses may have a better safety profile after intravenous injection compared with Ad5-based viruses.

Antiangiogenesis gene armed tumor-targeting adenovirus yields multiple antitumor activities in human HCC xenografts in nude mice

AIM

Gene therapy represents a promising therapeutic strategy for hepatocellular carcinoma (HCC). To improve the ratio of killing efficacy on tumor cells to side-effect on normal cells, we constructed an oncolytic adenovirus vector, AdSu-hE, expressing the human endostatin (hE) gene, in which the chimeric promoter of human epidermal growth factor receptor 2 enhancer and human telomerase reverse transcriptase promoter was used to control the adenoviral E1a gene.

METHODS

Tumor-selective replication of adenovirus AdSu-hE and its concomitant expression of endostatin were measured by 50% tissue culture infective dose method, fluorescent protein expression, Western blot and enzyme linked immunosorbent assay in cancer and normal cell lines. The antitumor efficacy was observed in nude mice bearing human HCCs.

RESULTS

The oncolytic adenovirus AdSu-hE replicated restrictedly in telomerase-positive cancer cells and resulted in oncolysis, but did not replicate in normal cell lines. Along with virus replication, AdSu-hE mediated 5-fold increased expression of endostatin in tumor cells compared with that in normal cells. Moreover, AdSu-hE expressed more endostatin in cancer cells than the non-replicative adenovirus vector Ad-hE. In vivo administration of the oncolytic adenovirus AdSu-hE into HCC-bearing nude mice produced a significant tumor reduction by synergistic effects of virus oncolysis and endostatin antiangiogenesis.

CONCLUSION

The oncolytic virus with antiangiogenesis gene driven by the chimeric promoter has an improved killing efficacy on tumor cells, and may be useful for cancer gene therapy.

Potent antitumor effect of interleukin-24 gene in the survivin promoter and retinoblastoma double-regulated oncolytic adenovirus

Interleukin (IL)-24 is an excellent therapeutic gene for cancer therapy. In this work, IL-24 was inserted into Ad.sp-E1A(Delta24), an oncolytic adenovirus with a 24-bp deletion in the E1A gene, which was driven by the survivin promoter to form Ad.sp-E1A(Delta24)-IL-24. Ad.sp-E1A(Delta24)-IL-24 has an excellent antitumor effect in vitro for human nasopharyngeal, liver, lung, and cervical carcinoma cell lines but does no or little damage to normal cell lines L-02 and WI38. Furthermore, it achieved nearly complete inhibition (although not elimination) of NCI-H460 lung carcinoma growth in nude mice. The antitumor efficacy of Ad.sp-E1A(Delta24)-IL-24 on NCI-H460 cells was clearly mediated by apoptosis, because it induced caspase-3 and poly(ADP-ribose) polymerase cleavage. This is the first report of Ad.sp-E1A(Delta24)-IL-24 with such an excellent, broad, and specific antitumor effect in vitro and nearly complete inhibition of lung tumor growth in vivo.

Antitumor activity of Ad-IU2, a prostate-specific replication-competent adenovirus encoding the apoptosis inducer, TRAIL

In this study, we investigated the preclinical utility and antitumor efficacy of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) delivered by Ad-IU2, a prostate-specific replication-competent adenovirus (PSRCA), against androgen-independent prostate cancer. Through transcriptional control of adenoviral early genes E1a, E1b and E4, as well as TRAIL by two bidirectional prostate-specific enhancing sequences (PSES), expression of TRAIL as well adenoviral replication was limited to prostate-specific antigen (PSA) and prostate-specific membrane antigen (PSMA)-positive cells. Ad-IU2 induced 5-fold greater apoptosis selectively in PSA/PSMA-positive CWR22rv and C4-2 cells than an oncolytic adenoviral control. Furthermore, prolonged infection with Ad-IU2 reversed TRAIL resistance in LNCaP cells. Ad-IU2 exhibited superior killing efficiency in PSA/PSMA-positive prostate cancer cells at doses 5- to 8-fold lower than required by a PSRCA to produce a similar effect. This cytotoxic effect was not observed in non-prostatic cells, however. As an enhancement of its therapeutic efficacy, Ad-IU2 exerted a TRAIL-mediated bystander effect through direct cell-to-cell contact and soluble factors such as apoptotic bodies. In vivo, Ad-IU2 markedly suppressed the growth of subcutaneous androgen-independent CWR22rv xenografts compared to a PSRCA at six weeks post-treatment (3.1- vs. 17.1-fold growth of tumor). This study demonstrates the potential clinical utility of a PSRCA armed with an apoptosis-inducing ligand.

Targeting cancer by transcriptional control in cancer gene therapy and viral oncolysis

Cancer-specificity is the key requirement for a drug or treatment regimen to be effective against malignant disease--and has rarely been achieved adequately to date. Therefore, targeting strategies need to be implemented for future therapies to ensure efficient activity at the site of patients' tumors or metastases without causing intolerable side-effects. Gene therapy and viral oncolysis represent treatment modalities that offer unique opportunities for tumor targeting. This is because both the transfer of genes with anti-cancer activity and viral replication-induced cell killing, respectively, facilitate the incorporation of multiple mechanisms restricting their activity to cancer. To this end, cellular mechanisms of gene regulation have been successfully exploited to direct therapeutic gene expression and viral cell lysis to cancer cells. Here, transcriptional targeting has been the role model and most widely investigated. This approach exploits cellular gene regulatory elements that mediate cell type-specific transcription to restrict the expression of therapeutic genes or essential viral genes, ideally to cancer cells. In this review, we first discuss the rationale for such promoter targeting and its limitations. We then give an overview how tissue-/tumor-specific promoters are being identified and characterized. Strategies to apply and optimize such promoters for the engineering of targeted viral gene transfer vectors and oncolytic viruses-with respect to promoter size, selectivity and activity in the context of viral genomes-are described. Finally, we discuss in more detail individual examples for transcriptionally targeted virus drugs. First highlighting oncolytic viruses targeted by prostate-specific promoters and by the telomerase promoter as representatives of tissue-targeted and pan-cancer-specific virus drugs respectively, and secondly recent developments of the last two years.

Transthyretin-driven oncolytic adenovirus suppresses tumor growth in orthotopic and ascites models of hepatocellular carcinoma

Strategies to increase antitumor efficacy of oncolytic adenoviruses are actively investigated. We have previously shown that E1B-55 kDa-deleted adenovirus, designated Ad5WS1, has therapeutic potential for treating hepatocellular carcinoma (HCC). To achieve HCC-restricted replication of oncolytic adenovirus, we generated Ad5WS2, an E1B-55 kDa-deleted adenovirus with its E1A gene driven by the liver-specific transthyretin promoter. Our results showed that Ad5WS2 could replicate within tumor cells where the transthyretin gene was expressed. Mouse transthyretin promoter was active in murine and human HCC cells, but relatively quiescent in cells of non-liver origin. Ad5WS2 caused severe cytolytic effect on HCC cells, but was much attenuated in non-HCC cells. Peritoneal administration of Ad5WS2 into mice bearing liver tumors grown in ascites resulted in enhanced survival. In an orthotopic HCC model, Ad5WS2, when systemically administered, exerted higher antitumor effects than Ad5WS1. Lack of viral replication in normal organs and minimal hepatic toxicity was noted after Ad5WS2 treatment. Furthermore, the antitumor effect of Ad5WS2 could be enhanced when combined with chemotherapeutic agent cisplatin in the ascites tumor model. These results suggest that E1B-55 kDa-deleted adenovirus driven by the transthyretin promoter may be a safer and more efficacious oncolytic agent for the treatment of primary and metastatic HCC.

Intratumoral coadministration of hyaluronidase enzyme and oncolytic adenoviruses enhances virus potency in metastatic tumor models

PURPOSE

Evaluate the codelivery of hyaluronidase enzyme with oncolytic adenoviruses to determine whether it improves the spread of the virus throughout tumors, thereby leading to a greater overall antitumor efficacy in tumor models.

EXPERIMENTAL DESIGN

The optimal dose of hyaluronidase that provided best transduction efficiency and spread of a green fluorescent protein (GFP)-expressing adenovirus within tumors was combined with oncolytic viruses in tumor models to determine whether the combination treatment results in an improvement of antitumor efficacy.

RESULTS

In mice injected with the adenovirus Ad5/35GFP and an optimal dose of hyaluronidase (50 U), a significant increase in the number of GFP-expressing cells was observed when compared with animals injected with virus only (P < 0.0001). When the oncolytic adenoviruses Ad5OV or Ad5/35 OV (OV-5 or OV5T35H) were codelivered with 50 U of hyaluronidase, a significant delay in tumor progression was observed, which translated into a significant increase in the mean survival time of tumor-bearing mice compared with either of the monotherapy-treated groups (P < 0.0001). Furthermore, the mice that received the combination of Ad5/35 OV and hyaluronidase showed the best antitumor efficacy. Importantly, the combination treatment did not increase the metastatic potential of the tumors. Lastly, the increase in virus potency observed in animals injected with both enzyme and virus correlated with enhanced virus spread throughout tumors.

CONCLUSION

Antitumor activity and overall survival of mice bearing highly aggressive tumors are significantly improved by codelivery of oncolytic adenoviruses and hyaluronidase when compared with either of the monotherapy-treated groups, and it may prove to be a potent and novel approach to treating patients with cancer.

Enhanced combined tumor-specific oncolysis and suicide gene therapy for prostate cancer using M6 promoter

Enzyme pro-drug suicide gene therapy has been hindered by inefficient viral delivery and gene transduction. To further explore the potential of this approach, we have developed AdIU1, a prostate-restricted replicative adenovirus (PRRA) armed with the herpes simplex virus thymidine kinase (HSV-TK). In our previous Ad-OC-TK/ACV phase I clinical trial, we demonstrated safety and proof of principle with a tissue-specific promoter-based TK/pro-drug therapy using a replication-defective adenovirus for the treatment of prostate cancer metastases. In this study, we aimed to inhibit the growth of androgen-independent (AI), PSA/PSMA-positive prostate cancer cells by AdIU1. In vitro the viability of an AI- PSA/PSMA-expressing prostate cancer cell line, CWR22rv, was significantly inhibited by treatment with AdIU1 plus GCV (10 microg ml(-1)), compared with AdIU1 treatment alone and also cytotoxicity was observed following treatment with AdIU1 plus GCV only in PSA/PSMA-positive CWR22rv and C4-2 cells, but not in the PSA/PSMA-negative cell line, DU-145. In vivo assessment of AdIU1 plus GCV treatment revealed a stronger therapeutic effect against CWR22rv tumors in nude mice than treatment with AdIU1 alone, AdE4PSESE1a alone or in combination with GCV. Our results demonstrate the therapeutic potential of specific-oncolysis and suicide gene therapy for AI-PSA/PSMA-positive prostate cancer gene therapy.

Tightly regulated gene expression in human hematopoietic stem cells after transduction with helper-dependent Ad5/35 vectors

OBJECTIVE

Inducible and transient expression of transcription factors, growth factors, or mitogenic factors can be used to influence proliferation or differentiation of hematopoietic progenitor/stem cells (HSC). Furthermore, transient expression of proteins with site-specific endonuclease activity, potentially, can support targeted integration of exogenous transgenes into specific sites in the genome, a task that is currently a focus in development of gene therapy vectors.

MATERIALS AND METHODS

We constructed a set of helper-dependent adenovirus (Ad) vectors with serotype 35 fiber knob domains (HD-Ad5/35), which can efficiently transduce human CD34(+) cells, particularly subsets with potential stem cell capacity. These vectors contain Tet-inducible expression systems that were shielded by insulators and transcription stop signals to minimize unspecific interference by transcriptional elements present in viral and stuffer DNA. We compared two vectors, containing a fusion between the Krüppel-associated box (KRAB) domain and the tetracycline repressor (HD-Ad5/35.Tet-1) or an autoregulated rtTA (HD-Ad5/35.Tet-2) for regulated transgene expression in Mo7e cells, a model for HSC, and primary human CD34(+) cells.

RESULTS

HD-Ad5/35.Tet-1 conferred lower background expression than HD-Ad5/35.Tet-2, although levels of induced gene expression were higher for HD-Ad5/35.Tet-2. In CD34(+) cells, while HD-Ad5/35.Tet-1 allowed for activated gene expression in all transduced cells, induced gene expression from HD-Ad5/35.Tet-2 was restricted to a small subset of CD34(+) cells. Importantly, clonogeneic assays and repopulation studies in nonobese diabetic/severe combined immunodeficient mice showed that both HD-Ad5/35.Tet-1 and -2 vectors mediated induced gene expression in primitive hematopoietic cells. These studies also confirmed that transduction of CD34(+) cells with HD-Ad5/35 vectors is not associated with cytotoxicity, a problem observed with first-generation Ad5/35 vectors.

CONCLUSIONS

Both HD-Ad5/35 vector expression systems confer tightly regulated, transient transgene expression in human HSC.

Molecular therapy and prevention of liver diseases

Molecular analyses have become an integral part of biomedical research as well as clinical medicine. The definition of the molecular and genetic basis of many human diseases has led to a better understanding of their pathogenesis and has in addition offered new perspectives for their diagnosis, therapy and prevention. Genetically, liver diseases can be classified as hereditary monogenic, acquired monogenic, complex genetic and diseases. Based on this classification, gene therapy is based on six concepts: gene repair, gene substitution, cell therapy, block of gene expression or function, DNA vaccination as well as gene augmentation. While recent developments are promising, various delivery, targeting and safety issues need to be addressed before gene therapy will enter clinical practice. In the future, molecular diagnosis and therapy liver diseases will be part of our patient management and complement existing diagnostic, therapeutic and preventive strategies.