Anchoring of self-assembled plasmid DNA/anti-DNA antibody/cationic lipid micelles on bisphosphonate-modified stent for cardiovascular gene delivery

Stent-Based Gene Delivery for Coronary Disease

Percutaneous coronary interventions (PCI) are the mainstay for treatment of advanced coronary disease. A majority of PCI involve deployment of a stent in the affected vascular segment. This chapter introduces the concept of using stents as a platform for delivering gene therapies to the vasculature with the overarching aim of mitigating in-stent restenosis (ISR), late stent thrombosis (LST), and neoatherosclerosis (NA), a triad of delayed complications that reduce the overall success rate of PCI. The chapter provides a detailed methodology for coatless reversible attachment of adenoviral (Ad) and adeno-associated viral (AAV) vectors to the metal stent struts along with representative in vitro and in vivo results.

Gene Delivery from Stents for Prevention of In-Stent Restenosis

The increasing sophistication of vascular stent design, especially devices that combine mechanical support with local drug delivery to the vascular wall, has resulted in major progress in the management of coronary and peripheral artery disease. This progress is reflected in expanded anatomical and clinical indications for stent angioplasty, with complementary reduction in bypass surgery rates and decreased need for target-lesion revascularisation. Nevertheless, even with second-generation drug-eluting stents (DES), the most common cause of stent failure, in-stent restenosis, while <10%, generates high numbers of cases due to the large scale of stent use (there are >1 million stent angioplasty procedures yearly in the USA alone). Gene-eluting stents (GES), the next generation of stent devices now in the preclinical phase of development, have evolved over the past two decades around the concept of localised vessel wall delivery of gene vectors attached to the stent struts. GES potentially provide several important advantages over DES, such as prolonged or even permanent anti-restenotic effect, capacity to deliver dissimilar impact on smooth muscle cells and endothelium, and fine-tuning of transgene expression and pharmacological effect with systemically administered therapeutics. Furthermore, GES can be used for treating non-occlusive lesions with the aim of slowing the underlying atherosclerotic process in the vessel wall. GES research at this time is concerned with achieving effective and safe transgene overexpression in the stented arteries, optimal vector choice, and proper techniques for vector immobilisation on the stent struts.

MicroRNA delivery for regenerative medicine

MicroRNA (miRNA) directs post-transcriptional regulation of a network of genes by targeting mRNA. Although relatively recent in development, many miRNAs direct differentiation of various stem cells including induced pluripotent stem cells (iPSCs), a major player in regenerative medicine. An effective and safe delivery of miRNA holds the key to translating miRNA technologies. Both viral and nonviral delivery systems have seen success in miRNA delivery, and each approach possesses advantages and disadvantages. A number of studies have demonstrated success in augmenting osteogenesis, improving cardiogenesis, and reducing fibrosis among many other tissue engineering applications. A scaffold-based approach with the possibility of local and sustained delivery of miRNA is particularly attractive since the physical cues provided by the scaffold may synergize with the biochemical cues induced by miRNA therapy. Herein, we first briefly cover the application of miRNA to direct stem cell fate via replacement and inhibition therapies, followed by the discussion of the promising viral and nonviral delivery systems. Next we present the unique advantages of a scaffold-based delivery in achieving lineage-specific differentiation and tissue development.

Stent-mediated gene delivery for site-specific transgene administration to the airway epithelium and management of tracheobronchial tumors

BACKGROUND

Gene therapy is currently under investigation as a means of managing a variety of pulmonary diseases. Unfortunately, gene transfer to bronchial epithelium has been hampered by the lack of stable and efficient transduction. Recent studies have shown that gene vectors could be tethered to the metallic surfaces of intra-arterial stents. This approach enables efficacious and site-specific adenoviral gene delivery to the vascular endothelium.

OBJECTIVES

We hypothesized that airway mesh stents impregnated with viral gene vectors could be used for local gene delivery to benign and malignant bronchial epithelium.

METHODS

Serotype 5 adenoviral vectors (Ad5, E1-/E3-) containing the reporter genes green fluorescent protein (Ad.GFP) or β-galactoside/LacZ (Ad.LacZ), or a therapeutic gene, Ad.INF-β, were coupled to either metallic mesh disks or stents via anti-Ad knob antibodies. These platforms were assessed for their ability to transfect bronchial epithelial cells from both rats and humans, as well as murine (L1C2) and human (A549) lung cancer cell lines. Gene transfer was quantified by fluorescent microscopy, scanning fluorimetry for Ad.GFP, and light microscopy studies assessing β-galactosidase staining for Ad.LacZ. Metallic mesh and stent-mediated gene transfer was also performed in a murine flank tumor model and in a rat endotracheal tumor model in order to evaluate the therapeutic potential.

RESULTS

In these studies, murine and human non-small cell lung cancer (NSCLC) cells were successfully transfected with reporter genes in vitro. Ad.LacZ-complexed mesh successfully transfected reporter genes into established murine flank NSCLC tumors. In addition, Ad.LacZ-tethered stents could effectively transfect both tracheobronchial epithelium and submucosal glands in rats. Similar epithelial transfection was achieved in ex vivo human bronchial epithelium. Pilot in vivo experimentation provided data supporting the concept that therapeutic genes could also be delivered with this technology. In additional pilot in vivo experiments, the growth of murine flank tumors was inhibited by placement of mesh disks coupled with Ad.muINF-β, and rats bearing endotracheal tumors demonstrated a trend towards prolonged survival with insertion of Ad.ratINF-β-tethered stents.

CONCLUSIONS

Stent-mediated gene delivery successfully enabled site-specific vector administration to target rat and human airway cells in cell culture, organ culture and in vivo. Local tracheobronchial gene delivery via stents could provide a viable clinical solution for overcoming the difficulties encountered with vector delivery within the lungs, in particular by lowering requisite vector titers and by directing desired vectors to areas of interest. This strategy may prove valuable for treating tumors involving the tracheobronchial tree, as well as other nonmalignant tracheobronchial disorders.

Vascular gene transfer from metallic stent surfaces using adenoviral vectors tethered through hydrolysable cross-linkers

In-stent restenosis presents a major complication of stent-based revascularization procedures widely used to re-establish blood flow through critically narrowed segments of coronary and peripheral arteries. Endovascular stents capable of tunable release of genes with anti-restenotic activity may present an alternative strategy to presently used drug-eluting stents. In order to attain clinical translation, gene-eluting stents must exhibit predictable kinetics of stent-immobilized gene vector release and site-specific transduction of vasculature, while avoiding an excessive inflammatory response typically associated with the polymer coatings used for physical entrapment of the vector. This paper describes a detailed methodology for coatless tethering of adenoviral gene vectors to stents based on a reversible binding of the adenoviral particles to polyallylamine bisphosphonate (PABT)-modified stainless steel surface via hydrolysable cross-linkers (HC). A family of bifunctional (amine- and thiol-reactive) HC with an average t1/2 of the in-chain ester hydrolysis ranging between 5 and 50 days were used to link the vector with the stent. The vector immobilization procedure is typically carried out within 9 hr and consists of several steps: 1) incubation of the metal samples in an aqueous solution of PABT (4 hr); 2) deprotection of thiol groups installed in PABT with tris(2-carboxyethyl) phosphine (20 min); 3) expansion of thiol reactive capacity of the metal surface by reacting the samples with polyethyleneimine derivatized with pyridyldithio (PDT) groups (2 hr); 4) conversion of PDT groups to thiols with dithiothreitol (10 min); 5) modification of adenoviruses with HC (1 hr); 6) purification of modified adenoviral particles by size-exclusion column chromatography (15 min) and 7) immobilization of thiol-reactive adenoviral particles on the thiolated steel surface (1 hr). This technique has wide potential applicability beyond stents, by facilitating surface engineering of bioprosthetic devices to enhance their biocompatibility through the substrate-mediated gene delivery to the cells interfacing the implanted foreign material.

Endovascular Gene Delivery from a Stent Platform: Gene- Eluting Stents

A synergistic impact of research in the fields of post-angioplasty restenosis, drug-eluting stents and vascular gene therapy over the past 15 years has shaped the concept of gene-eluting stents. Gene-eluting stents hold promise of overcoming some biological and technical problems inherent to drug-eluting stent technology. As the field of gene-eluting stents matures it becomes evident that all three main design modules of a gene-eluting stent: a therapeutic transgene, a vector and a delivery system are equally important for accomplishing sustained inhibition of neointimal formation in arteries treated with gene delivery stents. This review summarizes prior work on stent-based gene delivery and discusses the main optimization strategies required to move the field of gene-eluting stents to clinical translation.