Site specific gene delivery in the cardiovascular system

Controlling the surface-mediated release of DNA using 'mixed multilayers'

We report the design of erodible 'mixed multilayer' coatings fabricated using plasmid DNA and combinations of both hydrolytically degradable and charge-shifting cationic polymer building blocks. Films fabricated layer-by-layer using combinations of a model poly(β-amino ester) (polymer 1) and a model charge-shifting polymer (polymer 2) exhibited DNA release profiles that were substantially different than those assembled using DNA and either polymer 1 or polymer 2 alone. In addition, the order in which layers of these two cationic polymers were deposited during assembly had a profound impact on DNA release profiles when these materials were incubated in physiological buffer. Mixed multilayers ∼225 nm thick fabricated by depositing layers of polymer 1/DNA onto films composed of polymer 2/DNA released DNA into solution over ∼60 days, with multi-phase release profiles intermediate to and exhibiting some general features of polymer 1/DNA or polymer 2/DNA films (e.g., a period of rapid release, followed by a more extended phase). In sharp contrast, 'inverted' mixed multilayers fabricated by depositing layers of polymer 2/DNA onto films composed of polymer 1/DNA exhibited release profiles that were almost completely linear over ∼60-80 days. These and other results are consistent with substantial interdiffusion and commingling (or mixing) among the individual components of these compound materials. Our results reveal this mixing to lead to new, unanticipated, and useful release profiles and provide guidance for the design of polymer-based coatings for the local, surface-mediated delivery of DNA from the surfaces of topologically complex interventional devices, such as intravascular stents, with predictable long-term release profiles.

Virus immobilization on biomaterial scaffolds through biotin-avidin interaction for improving bone regeneration

To spatially control therapeutic gene delivery for potential tissue engineering applications, a biotin-avidin interaction strategy was applied to immobilize viral vectors on biomaterial scaffolds. Both adenoviral vectors and gelatin sponges were biotinylated and avidin was applied to link them in a virus-biotin-avidin-biotin-material (VBABM) arrangement. The tethered viral particles were stably maintained within scaffolds and SEM images illustrated that viral particles were evenly distributed in three-dimensional (3D) gelatin sponges. An in vivo study demonstrated that transgene expression was restricted to the implant sites only and transduction efficiency was improved using this conjugation method. For an orthotopic bone regeneration model, adenovirus encoding BMP-2 (AdBMP2) was immobilized to gelatin sponges before implanting into critical-sized bone defects in rat calvaria. Compared to gelatin sponges with AdBMP2 loaded in a freely suspended form, the VBABM method enhanced gene transfer and bone regeneration was significantly improved. These results suggest that biotin-avidin immobilization of viral vectors to biomaterial scaffolds may be an effective strategy to facilitate tissue regeneration.

Adenoviral vector tethering to metal surfaces via hydrolyzable cross-linkers for the modulation of vector release and transduction

The use of arterial stents and other medical implants as a delivery platform for surface immobilized gene vectors allows for safe and efficient localized expression of therapeutic transgenes. In this study we investigate the use of hydrolyzable cross-linkers with distinct kinetics of hydrolysis for delivery of gene vectors from polyallylamine bisphosphonate-modified metal surfaces. Three cross-linkers with the estimated t1/2 of ester bonds hydrolysis of 5, 12 and 50 days demonstrated a cumulative 20%, 39% and 45% vector release, respectively, after 30 days exposure to physiological buffer at 37 °C. Transgene expression in endothelial and smooth muscles cells transduced with substrate immobilized adenovirus resulted in significantly different expression profiles for each individual cross-linker. Furthermore, immobilization of adenoviral vectors effectively extended their transduction effectiveness beyond the initial phase of release. Transgene expression driven by adenovirus-tethered stents in rat carotid arteries demonstrated that a faster rate of cross-linker hydrolysis resulted in higher expression levels at day 1, which declined by day 8 after stent implantation, while inversely, slower hydrolysis was associated with increased arterial expression at day 8 in comparison with day 1. In conclusion, adjustable release of transduction-competent adenoviral vectors from metallic surfaces can be achieved, both in vitro and in vivo, through surface immobilization of adenoviral vectors using hydrolyzable cross-linkers with structure-specific release kinetics.

Polyelectrolyte multilayers promote stent-mediated delivery of DNA to vascular tissue

We report an approach to deliver DNA to vascular tissue in vivo using intravascular stents coated with degradable, DNA-containing polyelectrolyte multilayers (PEMs). Ionically cross-linked multilayers ∼120 nm thick were fabricated layer-by-layer on the surfaces of balloon-mounted stainless steel stents using plasmid DNA and a hydrolytically degradable poly(β-amino ester) (polymer 1). Characterization of stents coated using a fluorescently end-labeled analog of polymer 1 revealed film erosion to be uniform across the surfaces of the stents; differential stresses experienced upon balloon expansion did not lead to faster film erosion or dose dumping of DNA in areas near stent joints when stents were incubated in physiologically relevant media. The ability of film-coated stents to transfer DNA and transfect arterial tissue in vivo was then investigated in pigs and rabbits. Stents coated with films fabricated using fluorescently labeled DNA resulted in uniform transfer of DNA to sub-endothelial tissue in the arteries of pigs in patterns corresponding to the locations and geometries of stent struts. Stents coated with films fabricated using polymer 1 and plasmid DNA encoding EGFP resulted in expression of EGFP in the medial layers of stented tissue in both pigs and rabbits two days after implantation. The results of this study, combined with the modular and versatile nature of layer-by-layer assembly, provide a polymer-based platform that is well suited for fundamental studies of stent-mediated gene transfer. With further development, this approach could also prove useful for the design of nonviral, gene-based approaches for prevention of complications that arise from the implantation of stents and other implantable interventional devices.

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

Purpose:

To investigate the anchoring of plasmid DNA/anti-DNA antibody/cationic lipid tri-complex (DAC micelles) onto bisphosphonate-modified 316 L coronary stents for cardiovascular site-specific gene delivery.

Methods:

Stents were first modified with polyallylamine bisphosphonate (PAA-BP), thereby enabling the retention of a PAA-BP molecular monolayer that permits the anchoring (via vector-binding molecules) of DAC micelles. DAC micelles were then chemically linked onto the PAA-BP-modified stents by using N-succinimidyl-3-(2-pyridyldithiol)-propionate (SPDP) as a crosslinker. Rhodamine-labeled DNA was used to assess the anchoring of DAC micelles, and radioactive-labeled antibody was used to evaluate binding capacity and stability. DAC micelles (encoding green fluorescent protein) were tethered onto the PAA-BP-modified stents, which were assessed in cell culture. The presence of a PAA-BP molecular monolayer on the steel surface was confirmed by X-ray photoelectron spectroscopy and atomic force microscope analysis.

Results:

The anchoring of DAC micelles was generally uniform and devoid of large-scale patches of defects. Isotopic quantification confirmed that the amount of antibody chemically linked on the stents was 17-fold higher than that of the physical adsorbed control stents and its retention time was also significantly longer. In cell culture, numerous green fluorescent protein-positive cells were found on the PAA-BP modified stents, which demonstrated high localization and efficiency of gene delivery.

Conclusion:

The DAC micelle-immobilized PAA-BP-modified stents were successful as a gene delivery system. Gene delivery using DAC micelle-tethered stent-based PAA-BP functionalization should be suitable for a wide array of single or multiple therapeutic gene strategies, and could be used on cardiovascular metallic implants for achieving efficient gene therapy.

Rapid release of plasmid DNA from surfaces coated with polyelectrolyte multilayers promoted by the application of electrochemical potentials

We report an approach to the rapid release of DNA based on the application of electrochemical potentials to surfaces coated with polyelectrolyte-based thin films. We fabricated multilayered polyelectrolyte films (or "polyelectrolyte multilayers", PEMs) using plasmid DNA and a model hydrolytically degradable cationic poly(β-amino ester) (polymer 1) on stainless steel substrates using a layer-by-layer approach. The application of continuous reduction potentials in the range of -1.1 to -0.7 V (vs a Ag/AgCl electrode) to film-coated electrodes in PBS at 37 °C resulted in the complete release of DNA over a period of 1-2 min. Film-coated electrodes incubated under identical conditions in the absence of applied potentials required 1-2 days for complete release. Control over the magnitude of the applied potential provided control over the rate at which DNA was released. The results of these and additional physical characterization experiments are consistent with a mechanism of film disruption that is promoted by local increases in pH at the film/electrode interface (resulting from electrochemical reduction of water or dissolved oxygen) that disrupt ionic interactions in these materials. The results of cell-based experiments demonstrated that DNA was released in a form that remains intact and able to promote transgene expression in mammalian cells. Finally, we demonstrate that short-term (i.e., non-continuous) electrochemical treatments can also be used to promote faster film erosion (e.g., over 1-2 h) once the potential is removed. Past studies demonstrate that PEMs fabricated using polymer 1 can promote surface-mediated transfection of cells and tissues in vitro and in vivo. With further development, the electrochemical approaches reported here could thus provide new methods for the rapid, triggered, or spatially patterned transfer of DNA (or other agents) from surfaces of interest in a variety of fundamental and applied contexts.

Degradable polyelectrolyte multilayers that promote the release of siRNA

We report an approach to the design of degradable polyelectrolyte-based films for the controlled release of siRNA from surfaces. Our approach is based on stepwise, layer-by-layer assembly of multilayered polyelectrolyte films (or "polyelectrolyte multilayers", PEMs) using siRNA and a hydrolytically degradable poly(β-amino ester) (polymer 1). Fabrication of films using siRNA sequences for green fluorescent protein (GFP) or firefly luciferase resulted in linear growth of ultrathin films (∼50 nm thick) that promoted the surface-mediated release of siRNA upon incubation in physiologically relevant media. Physicochemical characterization of these siRNA-containing films revealed large differences in film growth profiles, physical erosion profiles, and siRNA release profiles as compared to PEMs fabricated using polymer 1 and larger plasmid DNA constructs. For example, whereas films fabricated using plasmid DNA erode gradually and release DNA over a period of ∼48 h, films fabricated using siRNA released ∼65% of incorporated siRNA within the first hour of incubation, prior to the onset of any observed film erosion. This initial burst of release was followed by a second, slower phase of release (accompanied by gradual film erosion) over the next 23 h. These differences in release profiles and other behaviors likely result, at least in part, from large differences in the sizes of siRNA and plasmid DNA. Finally, we demonstrate that the siRNA in these films is released in a form that remains intact, functional, and able to silence targeted protein expression upon administration to mammalian cells in vitro. The results of this investigation provide a platform for the design of thin films and coatings that could be used to localize the release of siRNA from surfaces in a variety of fundamental and applied contexts (e.g., for development of new research tools or approaches to delivery from film-coated implants and other devices).

Surface immobilization of plasmid DNA with a cell-responsive tether for substrate-mediated gene delivery

The advancement of nonviral gene therapy hinges on the ability to exert highly specific spatial and temporal control of gene delivery systems to enable localized release of DNA. In this work, we have developed a system capable of promoting localized delivery of a plasmid by utilizing peptide nucleic acid (PNA) technology to bind DNA to a substrate via an enzymatically labile peptide sequence. The successful immobilization of the DNA to the model substrate as well as the specificity of the binding was confirmed with atomic force microscopy (AFM) and AFM-confocal overlay imaging. Fluorescence-based quantification revealed that surfaces treated with the conjugates had 49 ± 22 ng of DNA/cm(2), while there were 4.2 ± 2.1 ng of DNA/cm(2) on surfaces treated with unfunctionalized DNA. When NIH/3T3 cells were grown on the modified substrates, a significantly higher percentage of cells were transfected when the peptide tether was protease-sensitive as compared with when it was not labile. These results indicated that the peptide must be cleaved to release the DNA. In addition to providing cell-triggered release, this system decouples the properties of the complexation agent and the substrate from the method of immobilization/release to provide a model system that can be tailored to specific applications.

Release of DNA from polyelectrolyte multilayers fabricated using 'charge-shifting' cationic polymers: tunable temporal control and sequential, multi-agent release

We report an approach to the design of multilayered polyelectrolyte thin films (or 'polyelectrolyte multilayers', PEMs) that can be used to provide tunable control over the release of plasmid DNA (or multiple different DNA constructs) from film-coated surfaces. Our approach is based upon methods for the layer-by-layer assembly of DNA-containing thin films, and exploits the properties of a new class of cationic 'charge-shifting' polymers (amine functionalized polymers that undergo gradual changes in net charge upon side chain ester hydrolysis) to provide control over the rates at which these films erode and release DNA. We synthesized two 'charge-shifting' polymers (polymers 1 and 2) containing different side chain structures by ring-opening reactions of poly(2-alkenyl azlactone)s with two different tertiary amine functionalized alcohols (3-dimethylamino-1-propanol and 2-dimethylaminoethanol, respectively). Subsequent characterization revealed large changes in the rates of side chain ester hydrolysis for these two polymers; whereas the half-life for the hydrolysis of the esters in polymer 1 was ~200 days, the half-life for polymer 2 was ~6 days. We demonstrate that these large differences in side chain hydrolysis make possible the design of PEMs that erode and promote the surface-mediated release of DNA either rapidly (e.g., over ~3 days for films fabricated using polymer 2) or slowly (e.g., over ~1 month for films fabricated using polymer 1). We demonstrate further that it is possible to design films with release profiles that are intermediate to these two extremes by fabricating films using solutions containing different mixtures of these two polymers. This approach can thus expand the usefulness of these two polymers and achieve a broader range of DNA release profiles without the need to synthesize polymers with new structures or properties. Finally, we demonstrate that polymers 1 and 2 can be used to fabricate multilayered films with hierarchical structures that promote the sequential release of two different DNA constructs with separate and distinct release profiles (e.g., the release of a first construct over a period of ~3 days, followed by the sustained release of a second for a period of ~70 days). With further development, this approach could contribute to the design of functional thin films and surface coatings that provide sophisticated control over the timing and the order of the release of two or more DNA constructs (or other agents) of interest in a range of biomedical contexts.

In vitro and in vivo studies of local arterial gene delivery and transfection using lipopolyplexes-embedded stents

Gene-eluting stents can have profound impact in the treatment of coronary restenosis, especially when the encoded protein can re-endothelialize the arterial lumen. In this study, we have examined gene delivery in vitro and in vivo using poly(beta-amino ester) (PbAE) precondensed plasmid DNA-containing cationic liposomes or lipopolyplexes (LPP) immobilized on stainless steel meshes and stents using gelatin coatings. In vitro studies using LPP-immobilized on 50 mm round meshes using type A and B gelatin coatings showed that LPP were efficiently internalized in human aortic smooth muscle cells (SMC) over time, leading to green fluorescent protein (GFP) expression. Type B gelatin coating was found to be more effective in intracellular delivery and transgene expression efficiency and, as such, was used for stent coating. In vivo studies, carried out in iliac artery restenosis model in New Zealand white rabbits, also showed GFP expression in arterial tissues after 24 h of implantation. Based on these encouraging preliminary results, LPP-based formulations can serve as a safe and effective nonviral gene delivery system for effective treatment of coronary restenosis.

Digoxigenin modification of adenovirus to spatially control gene delivery from chitosan surfaces

To spatially control the delivery of multiple viral vectors from biomaterial scaffolds, digoxigenin (DIG) was conjugated to adenoviral capsid proteins as an antigenic determinant for antibody immobilization. The infectivity, toxicity, specificity and immobilization stability of DIG-modified adenovirus were examined to investigate the feasibility and effectiveness of this viral surface modification. Anti-DIG antibody conjugated on chitosan surfaces was able to immobilize DIG-modified adenovirus and could be stably bound on the material for at least two weeks, yet the modification was mild enough that viral infectivity was maintained. To immobilize two different adenoviruses, wax masking was applied to conjugate anti-DIG and anti-adenovirus antibodies in two discrete regions of a chitosan film. The distribution of these two viral vectors expressing different reporter genes was examined after cell culture. Fluorescent protein expression from transduced cells illustrated that the infection distribution could be controlled: one gene was delivered to the entire region of the biomaterial, and another was only delivered to defined regions. Compared to three other cardiac glycosides, ATPase inhibition was undetectable when DIG was conjugated on the adenovirus, suggesting that the method may be safe for in vivo application. This dual viral vector delivery system should be capable of generating distinct interfaces between cell signaling viruses to control tissue regeneration from a range of different biomaterials.

Multilayered polyelectrolyte assemblies as platforms for the delivery of DNA and other nucleic acid-based therapeutics

Materials that provide spatial and temporal control over the delivery of DNA and other nucleic acid-based agents from surfaces play important roles in the development of localized gene-based therapies. This review focuses on a relatively new approach to the immobilization and release of DNA from surfaces: methods based on the layer-by-layer assembly of thin multilayered films (or polyelectrolyte multilayers, PEMs). Layer-by-layer methods provide convenient, nanometer-scale control over the incorporation of DNA, RNA, and oligonucleotide constructs into thin polyelectrolyte films. Provided that these assemblies can be designed in ways that permit controlled film disassembly under physiological conditions, this approach can contribute new methods for spatial and/or temporal control over the delivery of nucleic acid-based therapeutics in vitro and in vivo. We describe applications of layer-by-layer assembly to the fabrication of DNA-containing films that can be used to provide control over the release of plasmid DNA from the surfaces of macroscopic objects and promote surface-mediated cell transfection. We also highlight the application of these methods to the coating of colloidal substrates and the fabrication of hollow micrometer-scale capsules that can be used to encapsulate and control the release or delivery of DNA and oligonucleotides. Current challenges, gaps in knowledge, and new opportunities for the development of these methods in the general area of gene delivery are discussed.

Delivery of large biopharmaceuticals from cardiovascular stents: a review

This review focuses on new and emerging large-molecule bioactive agents delivered from stent surfaces in drug-eluting stents (DESs) to inhibit vascular restenosis in the context of interventional cardiology. New therapeutic agents representing proteins, nucleic acids (small interfering RNAs and large DNA plasmids), viral delivery vectors, and even engineered cell therapies require specific delivery designs distinct from traditional smaller-molecule approaches on DESs. While small molecules are currently the clinical standard for coronary stenting, extension of the DESs to other lesion types, peripheral vasculature, and nonvasculature therapies will seek to deliver an increasingly sophisticated armada of drug types. This review describes many of the larger-molecule and biopharmaceutical approaches reported recently for stent-based delivery with the challenges associated with formulating and delivering these drug classes compared to the current small-molecule drugs. It also includes perspectives on possible future applications that may improve safety and efficacy and facilitate diversification of the DESs to other clinical applications.

Neoceptors: reengineering GPCRs to recognize tailored ligands

Efforts to model and reengineer the putative binding sites of G-protein-coupled receptors (GPCRs) have led to an approach that combines small-molecule 'classical' medicinal chemistry and gene therapy. In this approach, complementary structural changes (e.g. based on novel ionic or H-bonds) are made in the receptor and ligand for the selective enhancement of affinity. Thus, a modified receptor (neoceptor) is designed for activation by tailor-made agonists that do not interact with the native receptor. The neoceptor is no longer activated by the native agonist, but rather functions as a scaffold for the docking of novel small molecules (neoligands). In theory, the approach could verify the accuracy of GPCR molecular modeling, the investigation of signaling, the design of small molecules to rescue disease-related mutations, and small-molecule-directed gene therapy. The neoceptor-neoligand pairing could offer spatial specificity by delivering the neoceptor to a target site, and temporal specificity by administering neoligand when needed.

Gene therapy to create biological pacemakers

Old age and a variety of cardiovascular disorders may disrupt normal sinus node function. Currently, this is successfully treated with electronic pacemakers, which, however, leave room for improvement. During the past decade, different strategies to initiate pacemaker function by gene therapy were developed. In the search for a biological pacemaker, various approaches were explored, including beta(2)-adrenergic receptor overexpression, down regulation of the inward rectifier current, and overexpression of the pacemaker current. The most recent advances include overexpression of bioengineered ion channels and genetically modified stem cells. This review considers the strengths and the weaknesses of the different approaches and discusses some of the different viral vectors currently used.

Release of plasmid DNA from intravascular stents coated with ultrathin multilayered polyelectrolyte films

Materials that permit control over the release of DNA from the surfaces of topologically complex implantable devices, such as intravascular stents, could contribute to the development of new approaches to the localized delivery of DNA. We report the fabrication of ultrathin, multilayered polyelectrolyte films that permit both the immobilization and controlled release of plasmid DNA from the surfaces of stainless steel intravascular stents. Our approach makes use of an aqueous-based, layer-by-layer method for the assembly of nanostructured thin films consisting of alternating layers of plasmid DNA and a hydrolytically degradable polyamine. Characterization of coated stents using scanning electron microscopy (SEM) demonstrated that stents were coated uniformly with an ultrathin film ca. 120 nm thick that adhered conformally to the surfaces of stent struts. These ultrathin films did not crack, peel, or delaminate substantially from the surface after exposure to a range of mechanical challenges representative of those encountered during stent deployment (e.g., balloon expansion). Stents coated with eight bilayers of degradable polyamine and a plasmid encoding enhanced green fluorescent protein (EGFP) sustained the release of DNA into solution for up to four days when incubated in phosphate buffered saline at 37 degrees C, and coated stents were capable of mediating the expression of EGFP in a mammalian cell line without the aid of additional transfection agents. The approach reported here could, with further development, contribute to the development of localized gene-based approaches to the treatment of cardiovascular diseases or related conditions.

Ferrocene-containing cationic lipids for the delivery of DNA: Oxidation state determines transfection activity

The ability of two redox-active, ferrocene-containing cationic lipids [11-(ferrocenylundecyl)trimethylammonium bromide (FTMA) and bis(11-ferrocenylundecyl)dimethylammonium bromide (BFDMA)] to transfect mammalian cells was investigated. This study sought to determine the range of conditions over which these lipids were capable of transfecting cells and whether the oxidation state of the ferrocenyl groups in these materials could be used to influence the extent of transfection. Experiments conducted in the COS-7 cell line demonstrated that reduced and oxidized FTMA were substantially cytotoxic and did not transfect cells. Subsequent experiments conducted using BFDMA and reporter plasmids encoding enhanced green fluorescent protein (EGFP) and firefly luciferase demonstrated that BFDMA was able to transfect cells. However, the extent of transfection depended significantly upon both the concentration of BFDMA and the oxidation state of the lipid. Quantitative characterization of cytotoxicity and gene expression demonstrated that a window of concentration existed over which reduced BFDMA was non-cytotoxic and yielded high levels of transfection, but over which electrochemically oxidized BFDMA yielded very low (background) levels of transfection. Characterization of lipoplexes using dynamic light scattering demonstrated that reduced and oxidized BFDMA formed small aggregates (ca. 90 to 250nm) at concentrations of lipid ranging from 2 to 10 microM. Taken together, these results demonstrate that the oxidation state of BFDMA, which can be controlled electrochemically, can be used to control the extent of cell transfection. These results could form the basis of transfection procedures that exploit the redox behavior of ferrocene-containing lipids to achieve active spatial and temporal control over transfection using electrochemical methods.