Current Gene Therapy - Volume 3, Issue 5, 2003

Recently, stem cell research has attracted considerable attention because it could be used for the regeneration of damaged organs that are untreatable by conventional techniques, and several stem cells (or progenitor cells), such as endothelial stem cells and neural stem cells have been discovered. Following the progression of this field of research, the potential for stem cell gene therapy has increased and several therapeutic benefits have already been reported. Although this approach was originally investigated for fatal or hereditary diseases, chronic renal failure is also a candidate for stem cell gene therapy. We have proposed two different therapeutic strategies for chronic renal failure depending on whether the bone marrow stem cells differentiate and commit into mesenchymal or hematopoietic stem cells. In the case of diseases, which need reconstitution of residential renal cells, such as congenital enzyme deficiency diseases, mesenchymal stem cells should be transplanted, and in contrast, hematopoietic stem cells may be used for gene delivery for diseases, which need foreign cytokines and growth factors, such as glomerulonephritis. This article reviews the recent investigation on this tailor-made stem cell gene therapy for chronic renal failure and discusses the potential of this novel strategy and the major practical challenges of its clinical application.

Genomics and proteomics have unveiled a plethora of protein-protein interactions that may control cellular processes involved in disease development. Many of these interactions involve non-traditional candidate targets (i.e., neither enzymes nor cell surface receptors / channels). To date, non-traditional targets have largely been ignored by the pharmaceutical industry or have failed to lead to drugs. This review focuses on the use of transdominant genetically encoded agents and specialized small-molecule drugs to explore this void.

A conceptual breakthrough in gene therapy would be gene transfer vector that could be systemically applied, allowing targeted gene transfer into a predetermined cell type. The host range of a retroviral vector is determined by the interaction of the viral envelope glycoprotein (Env) and the retrovirus receptor on the surface of the host cell. In this review, we describe the current efforts to engineer targeted envelope glycoproteins, which can be incorporated into retroviral particles and are capable of delivering genes in a highly specific manner.

The use of anti-gene agents to disrupt the expression of disease-related genes could potentially be of utility in the treatment of a large number of illnesses, including most neoplasms. Traditional anti-gene agents include antisense oligonucleotides and ribozymes. Recent observations have provided evidence for another promising anti-gene technology-RNA interference (RNAi), in which the introduced double-stranded RNA (dsRNA), after a complicated series of processing steps, disrupts the expression of the targeted cellular gene. Further studies have indicated that small interfering RNAs (siRNAs) of generally 21 ∼ 23 nucleotides, which resemble the processing products of long dsRNA, can induce RNAi directly in mammalian cells. Because of their high specificity and efficiency, siRNAs might be a new class of anti-gene medicines for gene therapy applications.

Cardiovascular disease remains a major cause of morbidity and mortality in modern societies. While contemporary treatment modalities are making steady inroads to reduce this disease burden there remains a pressing need to vigorously explore novel therapeutic strategies. Rapid advances in our understanding of molecular pathology and the evolution of increasingly efficient gene transfer technology offer the imminent prospect of gene-based approaches to, at least, a subset of cardiovascular pathophysiologies. Initially envisaged as a treatment strategy for inherited monogenic disorders, it is now apparent that gene therapy has broader potential that encompasses acquired polygenic diseases, including many that affect the cardiovascular system. Extensive in vitro and animal studies are providing an increasingly sound scientific basis for cautious human evaluation. This review focuses on gene therapy of diseases primarily afflicting the heart, and provides an overview of gene and vector delivery systems with particular emphasis on systems suited to individual cardiac conditions. The pathophysiology underlying these conditions and molecular targets for therapeutic intervention are also reviewed.

Gene therapy is a translational science, with the ultimate goal of cancer gene therapy research being to develop effective and safe treatments for patients. In the new millennium, it is imperative to tailor a therapeutic strategy for a particular disease, based on clinical management issues. The desirable regulatory features and therapeutic strategies need to be fully considered before proceeding with molecular engineering of the gene delivery vector. Issues, such as celltargeted expression, in vivo monitoring of gene delivery and expression, therapeutic strategies, and vector selection that targets the particular disease stage should be addressed. During the validation phase of the study, an objective evaluation in relevant animal models should determine whether the vector meets the desired specifications. Meeting the predetermined criteria should propel the product towards the clinical phase of evaluation. This review will present the conceptual framework that has been applied to developing an integrated and targeted gene therapy for prostate cancer.

Although specific delivery to tissues and unique cell types in vivo has been demonstrated for many non-viral vectors, current methods are still inadequate for human applications, mainly because of limitations on their efficiencies. All the steps required for an efficient receptor-mediated gene transfer process may in principle be exploited to enhance targeted gene delivery. These steps are: DNA / vector binding, internalization, subcellular trafficking, vesicular escape, nuclear import, and unpacking either for transcription or other functions (i.e., antisense, RNA interference, etc.). The large variety of vector designs that are currently available, usually aimed at improving the efficiency of these steps, has complicated the evaluation of data obtained from specific derivatives of such vectors. The importance of the structure of the final vector and the consequences of design decisions at specific steps on the overall efficiency of the vector will be discussed in detail. We emphasize in this review that stability in serum and thus, proper bioavailability of vectors to their specific receptors may be the single greatest limiting factor on the overall gene transfer efficiency in vivo. We discuss current approaches to overcome the intrinsic instability of synthetic vectors in the blood. In this regard, a summary of the structural features of the vectors obtained from current protocols will be presented and their functional characteristics evaluated. Dissecting information on molecular conjugates obtained by such methodologies, when carefully evaluated, should provide important guidelines for the creation of effective, targeted and safe DNA therapeutics.

Protein transduction domains (PTDs, sometimes termed cell permeable proteins (CPP) or membrane translocating sequences (MTS)) are small peptides that are able to ferry much larger molecules into cells independent of classical endocytosis. This property makes PTDs ideal tools to transfer proteins and other molecules into living cells for research purposes. The mechanism by which this internalization takes place is poorly understood. It is evident, however, that many known PTDs bind to the same surface molecules (Heparan Sulphate Proteoglycans, HSPG) before internalization, and that internalization is dependent on these molecules. PTDs, although at this moment mainly used for the chemical or bacterial production of membrane permeable proteins can become powerful tools for gene therapy. By incorporating a PTD in the therapeutic gene product, the protein produced in the transfected cell might be enabled to spread to non-transfected cells, thereby creating an increased therapeutic effect. In this review, we give an overview of PTDs that may be useful for gene therapy applications, and discuss some of the problems that can be expected when incorporating PTDs in gene therapy approaches.