Distinct functions of retinoic acid receptor beta isoforms: implications for targeted therapy

Vitamin A is essential for development and differentiation of multiple tissues. Its derivatives, the retinoids, are potent drugs used to treat and prevent a variety of diseases. Retinoid effects are mediated by retinoic acid receptors (RARs) and retinoid X receptors (RXRs). There are three known RARs (alpha, beta, and gamma), and multiple isoforms of each receptor exist. Many of the therapeutic effects of retinoids including cancer chemoprevention and treatment of dermatologic disorders are mediated through RARbeta. In humans, five isoforms of this gene have been described. Specific isoforms of RARbeta exert distinct and sometimes opposing functions by altering patterns of target gene induction. Functional isoforms that activate distinct cassettes of target genes with differing biologic consequences include RARbeta1' and RARbeta2. Dominant negative isoforms of this gene that inhibit target gene activation include RARbeta4 and RARbeta5. RARbeta1 is poorly understood although this may function as an oncogene in certain cancers. Chromatin modifying drugs have been shown to trigger isoform-specific changes in the RARbeta gene. This review focuses on the structure and function of RARbeta isoforms as well as recent work in the epigenetic targeting of specific RARbeta isoforms. Discerning isoform-specific functions will be critical for exploiting the full potential of retinoid-based therapy including rational approaches to combining retinoids with chromatin modifying drugs.     

Genetic approaches for biologic therapy of cancer

Recently, there has been an increase in the types of biological therapeutic approaches developed for the treatment of cancer. This rapid advance in the biological therapy of cancer is due in part to advances in the field of molecular and cell biology as well as in the development of gene transfer systems. In particular, a better understanding of the mechanism of antigen presentation and T lymphocyte activation has resulted in the development of new immunotherapeutic strategies targeting tumor-associated antigens (TAA). The discovery of dendritic cells (DC) as potent antigen presenting cells and the development of methods for their use in immunotherapeutic regimens has led to novel approaches for treating cancer. Furthermore, the identification of genes encoding TAA and their peptide products, which are recognized by T lymphocytes in the context of major histocompatibility complexes class I and class II molecules, has led to the development of DNA-based vaccines against defined tumor antigens. Cytokines have been shown to be important adjuvant tools for immunization protocols by directing a T helper response favorable for an adequate cytotoxic T lymphocyte-mediated immune response. Novel gene transfer technologies have made it possible to employ a wide range of gene delivery systems, either viral or nonviral based, in anticancer therapies. Current immunotherapeutic strategies, including the use of DC transduced with genes coding for tumor antigens and cytokines delivered by recombinant viral vectors, have shown promise in animal tumor models.     

Scintigraphic imaging of HSVtk gene therapy

The evolution of molecular biology has enabled the exploration of novel sophisticated gene-directed treating modalities for cancer. Suicide gene therapy - i.e. transfection of a so-called suicide gene that sensitizes target cells towards a prodrug - may offer an attractive approach to treat malignant tumors. For the development of effective clinical suicide gene therapy protocols, a non-invasive method to assay the extent, the kinetics and the spatial distribution of transgene expression is essential. This would allow investigators and physicians to assess the efficiency of experimental and therapeutic gene transfection protocols and would enable early prognosis of therapy outcome. Radionuclide imaging techniques like single photon emission computed tomography (SPECT) and positron emission tomography (PET), which can non-invasively visualize and quantify metabolic processes in vivo, are being evaluated for repetitive monitoring of transgene expression in living animals and humans. Transgene expression can be monitored directly by imaging the expression of the therapeutic gene itself, or indirectly using a reporter gene that is coupled to the therapeutic gene. Various radiopharmaceuticals have been developed and are now being evaluated for imaging of transgene expression. This review surveys the progress that has been made in the field of non-invasive nuclear imaging of transgene expression and focuses on the herpes simplex virus type 1 thymidine kinase (HSVtk) gene therapy approaches.     

Gene therapy of benign gynecological diseases

Gene therapy is the introduction of genetic material into patient's cells to achieve therapeutic benefit. Advances in molecular biology techniques and better understanding of disease pathogenesis have validated the use of a variety of genes as potential molecular targets for gene therapy based approaches. Gene therapy strategies include: mutation compensation of dysregulated genes; replacement of defective tumor-suppressor genes; inactivation of oncogenes; introduction of suicide genes; immunogenic therapy and antiangiogenesis based approaches. Preclinical studies of gene therapy for various gynecological disorders have not only shown to be feasible, but also showed promising results in diseases such as uterine leiomyomas and endometriosis. In recent years, significant improvement in gene transfer technology has led to the development of targetable vectors, which have fewer side-effects without compromising their efficacy. This review provides an update on developing gene therapy approaches to treat common gynecological diseases such as uterine leiomyoma and endometriosis.     

New strategies and patent therapeutics in EBV-associated diseases

Epstein-Barr virus (EBV) is a virus present all throughout the world that causes infectious mononucleosis (IM) and is highly associated with certain malignancies. This study is a review of current knowledge concerning the pathogenic mechanisms of EBV in tumor and auto-immune diseases and the different new strategies to treat EBV associated pathologies. Phenomena surrounding the proliferation and immortalization of B lymphocytes, the mechanisms of immune escape and the role of CD8+ and CD4+ T cells in the infection by EBV are explained. An analysis is made of the role of EBV proteins during the biological events that take place in primary infection, persistent chronic infection together with an update of the approaches of novel patented therapeutics. Currently there is no vaccine protecting against EBV-associated disorders and no treatment that may inhibit or eliminate their progression. Thus, it is crucial to obtain additional information on the function and importance of genes that play a role on the development of those diseases with which it is associated, as well as on the humoral and cellular immune processes involved in them.     

Epstein–Barr virus: novel patented therapeutics

Importance of the field: Therapeutic strategies against Epstein–Barr virus (EBV) infection and associated cancers are still limited. Due to the primary role of this virus in the pathogenesis of these diseases, molecules interfering with EBV protein functions may represent effective therapeutic tools to treat EBV-associated diseases.

Areas covered in this review: Active immunotherapeutic protocols targeting EBV and EBV-associated cancers are reviewed first; then, we reviewed adoptive cellular therapies, innovative pharmacological approaches and other non-conventional therapeutic molecules.

What the reader will gain: The published literature, in particular patent publications on EBV therapeutic options, has been searched for relevant information. This information has been organized and discussed.

Take home message: Many promising therapeutic opportunities are identified. Among these, vaccination protocols and adoptive cellular therapies are the most advanced and reached Phase I/II clinical trials. Pharmacological approaches are at the moment limited to the laboratory phase.     

Epigenetic pathway targets for the treatment of disease: accelerating progress in the development of pharmacological tools: IUPHAR Review 11

The properties of a cell are determined both genetically by the DNA sequence of its genes and epigenetically through processes that regulate the pattern, timing and magnitude of expression of its genes. While the genetic basis of disease has been a topic of intense study for decades, recent years have seen a dramatic increase in the understanding of epigenetic regulatory mechanisms and a growing appreciation that epigenetic misregulation makes a significant contribution to human disease. Several large protein families have been identified that act in different ways to control the expression of genes through epigenetic mechanisms. Many of these protein families are finally proving tractable for the development of small molecules that modulate their function and represent new target classes for drug discovery. Here, we provide an overview of some of the key epigenetic regulatory proteins and discuss progress towards the development of pharmacological tools for use in research and therapy.     

Histone deacetylation : an attractive target for cancer therapy?

Recent research has elucidated another mechanism for gene expression and signalling protein regulation in malignant cells. Histone deacetylases (HDACs) have been associated with silencing of tumour suppressor genes, and with other functions that promote malignant cell phenotype, such as the function of the chaperone protein heat shock protein (HSP)-90. Malignant cells overexpress some HDACs, and aberrant gene products have been shown to recruit HDACs to DNA to accomplish silencing of differentiation in other genes. Several chemical classes of small molecule inhibitors of HDAC have been synthesized, including small chain fatty acids, benzamides, hydroxamic acids and hybrid molecules. All have shown preclinical activity in vitro and/or in vivo in nanomolar to micromolar concentrations. Some have shown activity in clinical trials. One (vorinostat; suberoylanalide hydroxamic acid [SAHA]) has been approved by the US FDA for therapy of T-cell lymphomas. HDAC inhibitors show the most promising activity as single agents in haematological malignancies rather than solid tumours. Clinical trials testing combinations of HDAC inhibitors with other antineoplastic agents and with demethylating agents have shown promising results. HDAC inhibitors also seem to enhance radiation effects on malignant tissue, while potentially sparing toxicity to normal tissues. In this article, we review the rationale for development of HDAC inhibitors as therapy for malignant diseases, as well as the preclinical and clinical trial data for some HDAC inhibitors under development.     

Gene therapy for cerebral vascular disease: update 2003

Gene therapy is a promising strategy for cerebrovascular diseases. Several genes that encode vasoactive products have been transferred via cerebrospinal fluid for the prevention of vasospasm after subarachnoid hemorrhage. Transfer of neuroprotective genes, including targeting of proinflammatory mediators, is a current strategy of gene therapy for ischemic stroke. Stimulation of growth of collateral vessels, stabilization of atherosclerotic plaques, inhibition of thrombosis, and prevention of restenosis are important objectives of gene therapy for coronary and limb arteries, but application of these approaches to carotid and intracranial arteries has received little attention. Several fundamental advances, including development of safer vectors, are needed before gene therapy achieves an important role in the treatment of cerebrovascular disease and stroke.     

Epigenetic events associated with breast cancer and their prevention by dietary components targeting the epigenome

Aberrant epigenetic alterations in the genome such as DNA methylation and chromatin remodeling play a significant role in breast cancer development. Since epigenetic alterations are considered to be more easily reversible compared to genetic changes, epigenetic therapy is potentially very useful in reversing some of these defects. Methylation of CpG islands is an important component of the epigenetic code, and a number of genes become abnormally methylated in breast cancer patients. Currently, several epigenetic-based synthetic drugs that can reduce DNA hypermethylation and histone deacetylation are undergoing preclinical and clinical trials. However, these chemicals are generally very toxic and do not have gene specificity. Epidemiological studies have shown that Asian women are less prone to breast cancer due to their high consumption of soy food than the Caucasian women of western countries. Moreover, complementary/and or alternative medicines are commonly used by Asian populations which are rich in bioactive ingredients known to be chemopreventive against tumorigenesis in general. Examples of such agents include dietary polyphenols, (-)-epigallocatechin-3-gallate (EGCG) from green tea, genistein from soybean, isothiocyanates from plant foods, curcumin from turmeric, resveratrol from grapes, and sulforaphane from cruciferous vegetables. These bioactive components are able to modulate epigenetic events, and their epigenetic targets are known to be associated with breast cancer prevention and therapy. This approach could facilitate the discovery and development of novel drugs for the treatment of breast cancer. In this brief review, we will summarize the epigenetic events associated with breast cancer and the potential of some of these bioactive dietary components to modulate these events and thus afford new therapeutic or preventive approaches.     

IL-12-Based therapy of malignancies

Interleukin-12 (IL-12) is an important molecule that triggers the activation of natural killer (NK) cells and T-cells, the development of T helper type 1 (Th1) cells and the expression of antiangiogenic genes. Novel methods for IL-12 delivery include cell-based ex vivo gene therapy, viral vector-based gene therapy and DNA plasmid-based nonviral gene therapy. IL-12 electroporation gene therapy may hold some promise for tumors accessible by electrode, such as head and neck cancer, breast cancer, prostate cancer and melanoma. Codelivery of other therapeutic genes with IL-12 may enhance the therapeutic effect and reduce the level of IL-12 required for efficacy. All three approaches to IL-12 gene therapy are under clinical investigation. The preliminary results indicate that IL-12 gene therapy is safe and is not associated with any major clinical toxicity. (c) 2001 Prous Science. All rights reserved.     

Synthetic sustained gene delivery systems

Gene therapy today is hampered by the need of a safe and efficient gene delivery system that can provide a sustained therapeutic effect without cytotoxicity or unwanted immune responses. Bolus gene delivery in solution results in the loss of delivered factors via lymphatic system and may cause undesired effects by the escape of bioactive molecules to distant sites. Controlled gene delivery systems, acting as localized depot of genes, provide an extended sustained release of genes, giving prolonged maintenance of the therapeutic level of encoded proteins. They also limit the DNA degradation in the nuclease rich extra-cellular environment. While attempts have been made to adapt existing controlled drug delivery technologies, more novel approaches are being investigated for controlled gene delivery. DNA encapsulated in nano/micro spheres of polymers have been administered systemically/orally to be taken up by the targeted tissues and provide sustained release once internalized. Alternatively, DNA entrapped in hydrogels or scaffolds have been injected/implanted in tissues/cavities as platforms for gene delivery. The present review examines these different modalities for sustained delivery of viral and non-viral gene-delivery vectors. Design parameters and release mechanisms of different systems made with synthetic or natural polymers are presented along with their prospective applications and opportunities for continuous development.