Longterm recombinant adeno-associated, virus-mediated, liver-generated expression of an angiogenesis inhibitor improves survival in mice with disseminated neuroblastoma

Gene Therapy Applications of Viral Vectors

Viral vectors have frequently been applied in gene therapy with the final goal of treating various diseases in the areas of neurology, neurodegeneration, metabolic disease, and cancer. Vectors have been engineered based on AAV, adenoviruses, alphaviruses, herpes simplex viruses, lentiviruses, and retroviruses. Some vectors are suitable for short-term episomal transgene expression, whereas others are integrated into the host cell genome to provide long-term expression. Additionally, hybrid vectors with favorable features from different viruses have been developed. Therapeutic genes of choice have typically been toxic genes such as thymidine kinase, pro-apoptotic genes like Bax, and immunostimulatory genes (for instance, interleukin-12). A large number of animal studies have demonstrated proof of concept of viral gene therapy. Many types of viral vectors have been employed in more than 700 clinical trials that have been carried out or are currently in progress.

Gene therapy as a potential tool for treating neuroblastoma-a focused review

Neuroblastoma, a solid tumor caused by rapid division of undifferentiated neuroblasts, is the most common childhood malignancy affecting children aged <5 years. Several approaches and strategies developed and tested to cure neuroblastoma have met with limited success due to different reasons. Many oncogenes are deregulated during the onset and development of neuroblastoma and thus offer an opportunity to circumvent this disease if the expression of these genes is restored to normalcy. Gene therapy is a powerful tool with the potential to inhibit the deleterious effects of oncogenes by inserting corrected/normal genes into the genome. Both viral and non-viral vector-based gene therapies have been developed and adopted to deliver the target genes into neuroblastoma cells. These attempts have given hope to bringing in a new regime of treatment against neuroblastoma. A few gene-therapy-based treatment strategies have been tested in limited clinical trials yielding some positive results. This mini review is an attempt to provide an overview of the available options of gene therapy to treat neuroblastoma.

Thioredoxin, thioredoxin-interacting protein and digestive diseases

The thioredoxin system is an antioxidative and redox-regulating system that consists of several small proteins, including thioredoxin (TRX), reduced coenzyme II (NADPH) and thioredoxin reductase (TRX-R). It can function to regulate oxidation-reduction state of cells, resist oxidative stress, activate transcription factors NF-κB and AP-1 to promote the growth and proliferation of cells, and interact with ASK-1 to inhibit apoptosis. Thioredoxin-interacting protein (TXNIP) is a member of the thioredoxin-binding protein family and plays a role in mediating oxidative stress, resisting cell proliferation and inducing apoptosis, acting as a negative regulator of the TRX system. Since oxidative stress and apoptosis are often involved in the pathogenesis of digestive diseases, TRX and TXNIP may play roles in the pathogenesis of digestive diseases. This paper gives an overview of the structure and functions of TRX and TXNIP and reviews the recent advances in understanding the relationship between the two proteins and digestive diseases.

Transcriptional targeting of tumor endothelial cells for gene therapy

It is well known that angiogenesis plays a critical role in the pathobiology of tumors. Recent clinical trials have shown that inhibition of angiogenesis can be an effective therapeutic strategy for patients with cancer. However, one of the outstanding issues in anti-angiogenic treatment for cancer is the development of toxicities related to off-target effects of drugs. Transcriptional targeting of tumor endothelial cells involves the use of specific promoters for selective expression of therapeutic genes in the endothelial cells lining the blood vessels of tumors. Recently, several genes that are expressed specifically in tumor-associated endothelial cells have been identified and characterized. These discoveries have enhanced the prospectus of transcriptionally targeting tumor endothelial cells for cancer gene therapy. In this manuscript, we review the promoters, vectors, and therapeutic genes that have been used for transcriptional targeting of tumor endothelial cells, and discuss the prospects of such approaches for cancer gene therapy.

The development of gene therapy: from monogenic recessive disorders to complex diseases such as cancer

During the last 4 decades, gene therapy has moved from preclinical to clinical studies for many diseases ranging from monogenic recessive disorders such as hemophilia to more complex diseases such as cancer, cardiovascular disorders, and human immunodeficiency virus (HIV). To date, more than 1,340 gene therapy clinical trials have been completed, are ongoing, or have been approved in 28 countries, using more than 100 genes. Most of those clinical trials (66.5%) were aimed at the treatment of cancer. Early hype, failures, and tragic events have now largely been replaced by the necessary stepwise progress needed to realize clinical benefits. We now understand better the strengths and weaknesses of various gene transfer vectors; this facilitates the choice of appropriate vectors for individual diseases. Continuous advances in our understanding of tumor biology have allowed the development of elegant, more efficient, and less toxic treatment strategies. In this introductory chapter, we review the history of gene therapy since the early 1960s and present in detail two major recurring themes in gene therapy: (1) the development of vector and delivery systems and (2) the design of strategies to fight or cure particular diseases. The field of cancer gene therapy experienced an "awkward adolescence." Although this field has certainly not yet reached maturity, it still holds the potential of alleviating the suffering of many individuals with cancer.

Potent antitumor effects of ZD6474 on neuroblastoma via dual targeting of tumor cells and tumor endothelium

Among children with relapsed or refractory neuroblastoma, the prognosis is poor and novel therapeutic strategies are needed to improve long-term survival. As with other solid tumors, high vascular density within neuroblastoma is associated with advanced disease, and therapeutic regimens directed against the tumor vasculature may provide clinical benefit. The receptor tyrosine kinase RET is widely expressed in neuroblastoma and is known to activate key signal transduction pathways involved in tumor cell survival and progression including Ras/mitogen-activated protein kinase and phosphatidylinositol 3-kinase/Akt. We investigated the effect of dual targeting of tumor cells and tumor endothelium with ZD6474, a small-molecule tyrosine kinase inhibitor of vascular endothelial growth factor (VEGF) receptor 2, epidermal growth factor receptor, and RET. ZD6474 inhibited the phosphorylation of RET in neuroblastoma cells and had a direct effect on tumor cell viability in seven neuroblastoma cell lines. In a human neuroblastoma xenograft model, ZD6474 inhibited tumor growth by 85% compared with treatment with vehicle alone. In contrast, no significant inhibition of tumor growth was observed after treatment with bevacizumab, an antihuman VEGF monoclonal antibody, or the epidermal growth factor receptor inhibitor erlotinib, either alone or in combination. Immunohistochemical analysis showed that ZD6474 treatment led to an increase in endothelial cell apoptosis along with inhibition of VEGF receptor-2 activation on tumor endothelium. In conclusion, dual targeting of tumor cells, potentially through RET inhibition, and tumor vasculature with ZD6474 leads to potent antitumor effects. This approach merits further investigation for patients with neuroblastoma.

Treatment of human disease by adeno-associated viral gene transfer

During the past decade, in vivo administration of viral gene transfer vectors for treatment of numerous human diseases has been brought from bench to bedside in the form of clinical trials, mostly aimed at establishing the safety of the protocol. In preclinical studies in animal models of human disease, adeno-associated viral (AAV) vectors have emerged as a favored gene transfer system for this approach. These vectors are derived from a replication-deficient, non-pathogenic parvovirus with a single-stranded DNA genome. Efficient gene transfer to numerous target cells and tissues has been described. AAV is particularly efficient in transduction of non-dividing cells, and the vector genome persists predominantly in episomal forms. Substantial correction, and in some instances complete cure, of genetic disease has been obtained in animal models of hemophilia, lysosomal storage disorders, retinal diseases, disorders of the central nervous system, and other diseases. Therapeutic expression often lasted for months to years. Treatments of genetic disorders, cancer, and other acquired diseases are summarized in this review. Vector development, results in animals, early clinical experience, as well as potential hurdles and challenges are discussed.

Delivery of antiangiogenic agents for cancer gene therapy

The understanding that tumor growth and metastasis are angiogenesis dependent processes has led to interest in targeting tumor vasculature in anticancer therapy. Furthermore, recent insights into the molecular interactions that orchestrate physiologic and pathologic angiogenesis have resulted in a variety of antiangiogenic strategies. A gene therapy-mediated approach for the delivery of antiangiogenic agents has several advantages, including the potential for sustained expression. However, the choice of angiogenesis inhibitor, method of gene delivery, and target/site for transgene expression are important variables to be considered when designing this approach. Here we review the major alternatives within each of these categories and provide illustrative examples of their use in preclinical models.

Adeno-associated virus vector-mediated delivery of pigment epithelium-derived factor restricts neuroblastoma angiogenesis and growth

PURPOSE

The purpose of this study was to evaluate the ability of adeno-associated virus (AAV) vector-mediated delivery of pigment epithelium-derived factor (PEDF) to inhibit neuroblastoma (NB) xenograft growth. Pigment epithelium-derived factor was chosen for this study because, in addition to being a potent inhibitor of angiogenesis, it is capable of inducing neuronal differentiation.

METHODS

Cohorts of mice received either recombinant AAV encoding human PEDF (rAAV-hPEDF) at a range of doses or control vector via tail vein. Subsequent hPEDF expression was measured by enzyme-linked immunoassay. After 6 weeks, the mice were given human NB cells by retroperitoneal injection and then killed 5 weeks later. Tumor weight, microvessel density, tumor differentiation, apoptosis, and levels of intratumoral vascular endothelial growth factor (VEGF) expression were determined at that time. In subsequent cohorts of mice, AAV-mediated murine PEDF expression was tested against both human NB xenografts and murine tumors.

RESULTS

In a series of in vitro studies, PEDF was shown to inhibit endothelial cell activation and to stimulate differentiation of NB cell lines. After tail vein injection of rAAV-hPEDF, stable transgene expression was generated and correlated with levels of vector administration. Human NB xenograft growth was restricted by hPEDF in a dose-dependent fashion. Intratumoral VEGF expression and microvessel density were decreased, and tumor cell apoptosis was increased in PEDF-treated mice.

CONCLUSIONS

Treatment with PEDF had a significant impact on NB growth in mice when delivered continuously using a gene therapy-mediated approach. The activity of PEDF appears to be mediated in part by inhibition of tumor-induced angiogenesis through down-regulation of tumor-elaborated VEGF, with subsequent intratumoral apoptosis. Furthermore, hPEDF was able to induce NB differentiation in vitro and in vivo. In addition, antitumor efficacy was seen when mouse PEDF was used to treat syngeneic murine tumors. In our murine models, gene therapy-mediated delivery of PEDF appears promising for the treatment of neuroblastoma.