These studies report on reversible attachment of adenoviral gene vectors to coatless metal surfaces of stents and model mesh disks. Sustained release of transduction-competent viral particles contingent upon hydrolysis of cross-linkers used for vector immobilization results in a durable site-specific transgene expression in vascular cells and in stented arteries.
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.
The effectiveness of gene therapy as a therapeutic modality is hampered by the poor targeting capacity of gene therapy vectors1,2. The lack of proper targeting results in sub-therapeutic levels of transgene expression at the target location and leads to a wide dissemination of vectors to non-target organs3, including those responsible for mounting immune responses against both the vector and encoded therapeutic product4,5. One potential means to offset the promiscuity of transduction and to promote targeting is to introduce gene vectors at the desired location in a form that precludes their free dissemination via blood and lymph. Typically, such efforts rely on a locally injectable delivery systems comprising of either viral or non-viral vectors admixed with fibrin, collagen or hyaluronic acid hydrogel matrices6-10 that are capable of transiently sustaining gene vectors at the injection site by physically entrapping them in a polymeric network.
Another generally accepted paradigm for localized gene therapy utilizes immobilization of gene vectors on the surface of implanted prosthetic devices11,12. Permanent medical implants (endovascular, bronchial, urological and gastrointestinal stents, pacemakers, artificial joints, surgical and gynecological meshes, etc.) are used yearly in tens of millions of patients13. While generally effective, these devices are prone to complications that are inadequately controlled for by current medical practices14-17. Implantable prosthetic devices present a unique opportunity to serve as proxy platforms for localized gene therapy treatment. From the pharmacokinetic standpoint, surface derivatization of medical implants with relatively low input doses of gene vectors results in achieving both high local concentrations of gene vectors on the implant/tissue interface and slowing the kinetics of their elimination from this location. As a consequence of protracted residence and enhanced uptake by the targeted cell population, vector immobilization minimizes spread of the gene vector. Thus the inadvertent inoculation of non-target tissues is reduced.
Surface tethering of gene vectors on implantable biomaterials (also termed as substrate-mediated gene delivery or solid phase gene delivery) has been implemented in cell culture and animal experiments using both specific (antigen-antibody18-20, avidin-biotin21,22) and non-specific23-26 (charge, van der Waals) interactions. The covalent attachment of vectors to the surface of the implanted device has been previously considered as non-functional since excessively strong bonds with the surface preclude vector internalization by target cells. Recently it was demonstrated that this limitation can be overcome through the use of spontaneously hydrolysable cross-linker used as the tethers between the modified metallic surface of the stent and capsid proteins of the adenoviral vector27,28. Moreover, the vector release rate and time course of transgene expression in vitro and in vivo can be modulated with the use of hydrolysable cross-linkers exhibiting different kinetics of hydrolysis28.
The present paper provides a detailed protocol for the reversible covalent attachment of adenoviral vectors to activated metal surface and introduces a useful experimental setup for studying ensuing transduction events in vitro in cultured smooth muscle and endothelial cells and in vivo in the rat carotid model of stent angioplasty.
The presented protocol describes an operational method for substrate mediated gene delivery achieved through reversible attachment of adenoviral vectors to coatless stainless steel surfaces. While developed for the specific purpose of stent-based gene therapy of vascular restenosis, this technique has much broader applications in the areas of biomaterials, biomedical implants and gene therapy.
Although presented studies have solely utilized stainless steel as a prototypical metal substrate, PA…
The authors have nothing to disclose.
The authors do not have competing financial interests to disclose.
316 stainless steel mesh disks | Electon Microscopy Sciences | E200-SS | |
Generic 304-grade stainless steel stents | Laserage | custom order | |
AdeGFP | University of Pennsylvania Vector Core | AD-5-PV0504 | |
AdLuc | University of Pennsylvania Vector Core | AD-5-PV1028 | |
AdEMPTY | University of Pennsylvania Vector Core | A858 | |
Cy3(NHS)2 | GE Healthcare | PA23000 | |
Sepharose 6B | Sigma-Aldrich | 6B100-500ML | |
UV 96-well plates | Costar | 3635 | |
Fluorometry 96-well plates | Costar | 3915 | |
Cell culture 96-well plates | Falcon | 353072 | |
Tris(2-carboxyethyl)phosphine hydrochloride (TCEP ) | Pierce Thermo Scientific | 20490 | |
dithiothreitol (DTT) | Pierce Thermo Scientific | 20290 | |
sulfo-LC-SPDP | Pierce Thermo Scientific | 21650 | |
Spectrophotometer | Molecular Devices | SpectraMax 190 | |
Spectrofluorometer | Molecular Devices | SpectraMax Gemini EM | |
Orbital shaker incubator | VWR | 1575R | |
Horizontal airflow oven | Shel Lab | 1350 FM | |
Centra-CL2 centrifuge | International Equipment Company | 426 | |
Digital vortex mixerer | Fisher Thermo Scientific | 02-215-370 | |
Eclipse TE300 fluorescence microscope | Nikon | TE300 | |
DC 500 CCD camera | Leica | DC-500 | |
7500 Real-Time PCR system | Applied Biosystems | not available | |
IVIS Spectrum bioluminescence station | Perkins-Elmer | not available | |
EDTA dipotassium salt | Sigma-Aldrich | ED2P | |
Bovine serum albumin fraction V (BSA) | Fisher Thermo Scientific | BP1600-100 | |
Tween-20 | Sigma-Aldrich | P1379 | |
Dumont forceps | Fine Science Tools | 11255-20 | |
A10 cell line | ATCC | CRL-1476 | |
Bovine aortic endothelial cells | Lonza | BW-6002 | |
Luciferin, potassium salt | Gold Biotechnology | LUCK-1Ge | |
Pluronic F-127 | Sigma-Aldrich | P2443-250G | |
PBS without calcium and magnesium | Gibco | 14190-136 | |
Fetal bovine serum | Gemini Bio-Products | 100-106 | |
Penicillin/Streptomycin solution | Gibco | 11540-122 | |
DMEM, high glucose | Corning cellgro | 10-013-CV | |
0.25% Trypsin/EDTA | Gibco | 25200-056 | |
QIAamp DNA micro kit | Qiagen | 56304 | |
Power Sybr Green PCR Master Mix | Applied Biosystems | 4367659 | |
MicroAmp Optical 96-well Reaction Plate | Applied Biosystems | N8010560 | |
MicroAmp Optical Adhesive Film | Applied Biosystems | 4360954 | |
Cephazolin | Apotex | not available | |
Loxicom (Meloxicam) | Norbrook | not available | |
Heparin sodium | APP Pharmaceuticals | not available | |
Ketavet (Ketamine) | VEDCO | not available | |
Anased (Xylazine) | Lloid | not available | |
Forane (Isoflurane) | Baxter | not available | |
Curved Moria iris forceps | Fine Science tools | 11370-31 | |
Curved extra-fine Graefe forceps | Fine Science Tools | 11152-10 | |
Dumont #5 forceps | Fine Science Tools | 11252-20 | |
Vannas spring scissors | Fine Science Tools | 15018-10 | |
Fine scissors – ToughCut | Fine Science Tools | 14058-09 | |
Surgical scissors | Fine Science Tools | 14101-14 | |
Vicryl suture (5-0) | Ethicon | J385 | |
Suture thread (4/0 silk) | Fine Science Tools | 18020-40 | |
Michel suture clips | Fine Science Tools | 12040-02 | |
Wound dilator (Lancaster eye specula) | KLS Martin | 34-149-07 | |
Hot bead sterilizer | Fine Science Tools | 18000-45 | |
Michel suture clip applicator | Fine Science Tools | 112028-12 | |
Insyte Autoguard 24G IV catheter | Beckton-Dickinson | 381412 | |
2F Fogarty catheter | Edwards Lifesciences | 120602F | |
Teflon tubing | Vention | 041100BST | |
PTA catheter | NuMed | custom order | |
Gauze pads | Kendall Healthcare | 9024 | |
Cotton applicators | Solon Manufacturing | WOD1003 | |
Saline | Baxter | 281321 | |
10 ml syringe (Luer-Lok) | Beckton-Dickinson | 309604 | |
1 ml syringe (Luer-Lok) | Beckton-Dickinson | 309628 | |
Clippers with #40 blade | Oster | 78005-314 | |
Transpore surgical tape | 3M | MM 15271 | |
Puralube vet ointment | Pharmaderm | not available |