Catálogo de publicaciones - libros

Over the past 25 yr, gene silencing therapy derived from nucleic acid-based molecules has evolved from bench research to clinical therapy. The recent discovery of RNA interference (RNAi), a mechanism by which double stranded RNAs mediate sequence-specific gene silencing, provided a new tool in the fight against cancer. The application of RNAi technology in basic cancer research will facilitate the identification and validation of potential therapeutic targets for cancer, and the elucidation of the molecular pathways governing cancer growth and development. RNAi technology could be further developed into therapeutics for cancer by selectively silencing aberrantly activated oncogenes. However, major challenges of delivery, specificity and efficacy need to be overcome before siRNAs can be used as therapeutic agents.

Adenovirus (Ad) has been applied for gene therapy in various applications. The current Ad vector system has two critical problems; low transduction of the target cancer cells and high transduction of nontarget normal organs. To address these issues, we have been working on “retargeting” of Ad vectors via transductional or transcriptional targeting. Transductional targeting has been achieved with application of various bridging moieties, genetical modification of vector capsid, or chemically coating viral particles. On the other hand, transcriptional targeting has been performed by employing natural or artificial transcriptional control elements with desired selectivity profile. In the field of cancer gene therapy, such retargeting has achieved augmented infectivity in the cancers that have been difficult to transduce with conventional Ad vector, as well as cancer specific transgene expression for avoiding toxicity. Success in cancer gene therapy requires vector design reflecting the pathological/physiological profile of the target disease, such as conditionally replicative adenovirus with combined retargeting mechanisms incorporated. In addition, we must continue to seek new targeting modalities because different tumor context always imposes unique challenges with respect to disease targeting. While reliable preclinical/clinical studies are necessary to establish a legitimate role of adenoviral retargeting in the field of cancer gene therapy, it is obvious that better vector targeting should leads to more potent and safe adenovirus based cancer therapeutics.

The use of viruses to treat human malignancy is not a new concept but has only recently evolved into a clinically viable therapy. Spurred by advances in molecular biology that have allowed relatively easy manipulation of the viral genome, a number of different viruses have been evaluated and shown to have promise as anticancer agents. Of these, herpes simplex virus (HSV) has been perhaps the most intensively investigated. Several strains of replication competent oncolytic HSV have been developed, some of which have been used in clinical trials. Continuing research efforts are aimed at manipulating the viral genome to more specifically target tumor cells, to further enhance efficacy while maintaining safety, and to assess the role of oncolytic HSV in combination with chemotherapy and radiation therapy.

This chapter will discuss the potential for delivery of cytokine molecules using neo-adjuvant/adjuvant gene therapy strategies to achieve antitumor efficacy. It focuses on two approaches for delivery of cytokine genes to achieve effective therapy; in situ delivery using adenoviral vectors also termed “active vaccination,” and cell based approaches using specific immune cells modified with cytokine genes. These approaches have potential advantages for prostate cancer therapy and possibly other genitourinary malignancies.

To date tremendous progress has been made in the field of cancer gene therapy. Strategies have been explored for achieving therapeutic benefit using various genes and several clinical trials for cancer gene therapy have been carried out demonstrating that gene therapy is well tolerated. However, in most cases the efficacy of gene transfer has been very limited. As an alternative, multimodality therapies are being developed with the idea of increasing the efficacy of the treatment, decreasing toxicity, and minimizing the development of resistance. Thus, simultaneous or sequential administration of gene therapy agents with conventional anticancer agents may work in a synergistic manner. Conventional radiotherapy is usually limited by a narrow therapeutic index and the combination of gene therapy with radiation is especially promising. Preclinical and clinical studies have, in fact, demonstrated significant potential for the combination of cancer gene therapy with radiotherapy that could lead to improved treatment responses. This chapter attempts to highlight some of the gene therapy approaches that have shown success both in preclinical models and in clinical trials when used in combination with conventional radiotherapy.

Hematopoietic stem cells (HSCs) have been the archetypal target for therapeutic gene transfer strategies, due to the ease with which these cells are obtained and cultured ex vivo, as well as their capacity for reconstituting an entire tissue type. The myelosuppressive consequence of neoplastic disease treatment has provided additional thrust for the development of HSC drug-resistance and gene transfer strategies. In this regard, significant advances in vector design have been achieved by careful evaluation of different promoter and enhancer sequences, as well as exogenous elements, that contribute to high gene expression levels and resist positional effect variegation. Gene transfer efficiencies have also been improved by the identification of envelope pseudotypes that recognize receptors expressed in the more primitive hematopoietic populations. In addition, several natural and synthetic gene products have been evaluated as tools for amplifying or enriching gene-modified HSCs in vivo. These include the homeobox transcription factors, selective amplifier genes, and drug resistance genes. The ability to enrich and repopulate the hematopoietic compartment with therapeutic gene-corrected cells requires strategies that act on primitive progenitor populations, and vectors that efficiently express multiple gene products. The realization of insertional mutagenesis has demonstrated the importance of therapy-related risk assessment and the need for vectors with inherent cell-type specificities. These advances have culminated in enhanced HSC gene transfer and enrichment, while highlighting areas requiring further development.

Genetic vaccination has tremendous potential for the treatment and prevention of cancer. This chapter briefly discusses the advances in research aimed at increasing the effectiveness of genetic vaccine formulations. Particular emphasis is placed on in vivo nonviral delivery technologies and modifications to safely achieve optimal antigen expression. We will also discuss implications for the future of genetic vaccines.

Angiogenesis and lymphangiogenesis play an important role in several normal and pathological conditions such as wound healing, reproduction, inflammation, and cancer growth and metastasis. A tight regulation between angiogenic/lymphangiogenic growth factors and inhibitors determines the balance between a progrowth or inhibitory phenotype. Hence, inhibition of angiogenesis/lymphangiogenesis using gene therapy is a potentially important strategy to inhibit the growth of primary tumors and to inhibit their metastatic spread. This chapter reviews the more recent data available in the field of angiogenesis/lymphangiogenesis. The focus of the chapter is on using gene therapy to achieve sustained physiological levels of antiangiogenic inhibitors with minimal systemic toxicity as well as ways to achieve tumor targeted antiangiogenic gene therapy.

Recent advances in the fundamental understanding of brain tumor biology have suggested that exploiting the molecular pathways underlying gliomagenesis may provide novel molecularly based approaches to brain tumor treatment. One such molecular approach is the application of replicationcompetent viruses as therapeutic agents for gliomas. With this approach, the capacity of viruses to infect, replicate within, and lyse cells is exploited to therapeutic advantage (oncolysis). In this context, by deleting 24 base pairs from the E1A gene, our group developed a conditionally replication-competent adenovirus, Δ 24. Because the mutant El A protein is unable to bind Rb (the critical protein involved in regulating entry into the cell cycle), Δ 24 selectively replicates in tumor cells, but not in normal cells with intact Rb. This chapter reviews the biology and therapeutic effects of Δ 24, and outlines modifications to this virus that have resulted in second-generation Δ 24 constructs that display increased tumor cell selectivity (Δ 24-RGD), reduced normal cell toxicity (CB1), and augmented tumoricidal capacity (Δ 24-CD and Δ 24-p53).

Genetic therapeutic agents have been tested in cancer patients for over 10 yr. Five major approaches have been tested in clinical trials: tumor suppressor gene replacement, prodrug-activating enzyme delivery, oncolytic virotherapy, antisense oligonucleotide delivery, and cytokine immuno-gene therapy. Proof-of-principle demonstrations of transgene expression, as well as certain biological activities, have been shown; serious toxicity has been rare. However, the field faces several challenges, including limited efficacy, side effects, and lack of proper response indicators. Inefficient tumor delivery and/or transfection, and rapid clearance mediated by host immune responses result in inadequate transgene expression and limited efficacy. Major side effects include vector-/transgene-specific toxicities and disease-/host-specific idiosyncrasy. Discrepancies between certain biomarkers and imaging studies also increase the difficulties in interpretation. Future cancer gene therapy agents need to incorporate mechanisms that allow us to further understand the biodistribution, expression, and function of the vector/transgene. Immune responses toward vectors and transgenes should be reduced, whereas antitumoral immune responses should be enhanced. Vectors and transgenes that offer more than one mechanisms-of-action need to be explored and combined. Finally, our understanding of tumor biology, vectorology and immunology needs to be strengthened in order to improve efficacy and minimizing toxicity.