1. Field of the Invention (Technical Field)
The present invention relates to coatings, methods of making and using coating compositions, and coated contacting surfaces of medical devices, wherein the coating includes a negatively-charged polymeric substrate forming a part of the coating surface, with a condensate complex of nucleic acid and a positively-charged polymer bound thereto by non-covalent means.
2. Background Art
Note that the following discussion refers to a number of publications by author(s) and year of publication, and that due to recent publication dates certain publications are not to be considered as prior art vis-a-vis the present invention. Discussion of such publications herein is given for more complete background and is not to be construed as an admission that such publications are prior art for patentability determination purposes.
There is a need for localized or regional (loco-regional) delivery of nucleic acids, such as DNA, for use in treatment of a variety of diseases by gene therapy and as a preventative or adjunct to other therapeutic modalities. However, systemic administration of DNA constructs, such as those including adenovirus vectors, frequently results in adverse consequences, and requires a substantially greater amount of gene construct than would be required with effective loco-regional transfection. In addition, for many conditions there is a need for controlled or sustained release of nucleic acids over a period of time, such that the gene construct may be continuously delivered. A number of methods and devices for gene transfection have been developed, but all involve significant limitations. There is thus a need for a biologically compatible method of loco-regional delivery of gene constructs, which may be incorporated and used with traditional implantable medical devices, or may be used with bioresorbable devices.
In the specific field of medical devices, use of medical devices, such as stents, catheters and the like, has been proposed to deliver nucleic acids that encode proteins or peptides directly related to the function of or recognized effects with medical devices. Thus, it has been proposed to utilize a device that delivers nucleic acid that encodes for fibroblast growth factor (FGF), platelet derived growth factor (PDGF), transforming growth factor (TGF), epidermal growth factor (EGF), vascular endothelial growth factor (VEGF), acidic fibroblast growth factor (aFGF), basic fibroblast growth factor (bFGF), fibroblast growth factor-5 (FGF-5) and the like, as disclosed in WO 01/41674, to M. Lahtinen, published Jun. 14, 2001. The WO 01/41674 reference employs a reservoir system for delivering nucleic acids, or alternatively binds nucleic acids, such as plasmids, to a xe2x80x9cglue compositionxe2x80x9d to immobilize the nucleic acids. Also of interest are genes such as nitric oxide synthetase, DNA constructs encoding interleukins, and genes that are introduced for gene-directed pro-drug therapy of cancer such as cytosine deaminase and uracil phosphoribosyltransferase.
It is generally known that nucleic acids, such as DNA, are naturally condensed in the nucleus of cells by histone proteins to form discrete structures termed nucleosomes. Nucleosomes, and the associated DNA, ultimately form chromosomes. There are five major types of histones, termed H1, H2a, H2B, H3, and H4. The histone proteins are rich in basic amino acids that contact negatively charged phosphate groups in DNA. DNA can also be condensed in vitro, through the use of polycations including isolated histones, polyornithine, polylysine, and the like to form a condensate. DNA is a highly negatively charged polymer, due to the repeating phosphate groups along the polymer backbone. With a cationic polymer such as polylysine a condensate is formed, presumptively through an electrostatic interaction between the DNA and polycation. This results in a complex of much smaller size that the original DNA molecule, which complex has exterior and accessible xe2x80x94NH2 charges. Very large genes can be condensed using this method, with genes as large as 45 kilobases employed. The size of a DNA and polycation complex forming a condensate is generally on the order of 50 to 300 nm in diameter, depending in part on the molecular weight of the DNA, size and character of the polycation, polycation molecular weight, salt concentration, temperature and the like. Condensates as small as 12 to 30 nm in diameter have been reported under optimal conditions.
The condensates are generally referred to as polyplexes (DNA/polymer complexes) and are being widely investigated as vehicles for gene therapy. One of the major limitations in polyplex-mediated gene delivery is the low circulation half-life of the polyplexes due to non-specific interactions such as those with extracellular matrices and non-target cell surfaces, clearance by the innate immune system, and aggregation at physiological salt conditions. The result of such non-specific interactions includes deposition in non-target organs such as the lung, as is disclosed in Verbaan F J, Oussoren C, van Dam I M, Takakura Y, Hashida M, Crommelin D J, Hennink W E, Storm G. The fate of poly(2-dimethyl amino ethyl)methacrylate-based polyplexes after intravenous administration. Int. J. Pharm. 214:99-101 (2001). Poly(ethylene glycol)-grafted (PEG) cationic polymers have shown promise by increasing the salt and serum stability of the resulting PEGylated polyplexes. However, PEGylation at high densities or PEGylation of low molecular weight cationic polymers usually prevents efficient DNA condensation by interfering with DNA binding.
A number of references disclose use of various systemic gene delivery systems. U.S. Pat. No. 5,166,320, to Wu and Wu, discloses a soluble DNA complex, comprising DNA bound to a polycation, which polycation is in term bound, by means of covalent bonds, to ligand specific for a cell surface receptor. This results in discrete molecular complexes which then bind a cell surface receptor. U.S. Pat. No. 5,614,503, to Chaudhary et al., discloses a nucleic acid transporter comprising a cationic compound having a cationic head group for binding the nucleic acid and a lipid tail for association with a cellular membrane. U.S. Pat. No. 5,837,533, to Boutin, discloses a multifunctional molecular complex including a cationic polyamide component, a fusogenic peptide, and a receptor-specific binding component. U.S. Pat. No. 6,312,727 discloses a synthetic polymer-based carrier vehicle including a cationic polymer forming a condensate with nucleic acid material reacted with a hydrophilic polymer material, resulting in a hydrophilic coating on the condensate. U.S. Patent Application No. 2001/10005717 discloses complexes of nucleic acid and polyethyleneimine, modified with a hydrophilic polymer covalently attached thereto. None of these methods, however, are adaptable to provide coatings for medical devices.
U.S. Pat. No. 5,788,959, to Singh, discloses a drug delivery device which comprises a single-phase matrix of two oppositely charged polymers. However, this device is not a component of a coating, the drugs disclosed therein do not include gene therapy drugs, such as nucleic acids, and no condensate or similar structure is formed.
U.S. Pat. Nos. 5,635,383 and 6,030,954, both to Wu and Wu, discloses a drug delivery formulation that comprises a soluble DNA-carrying complex formed by non-covalently binding a ligand conjugate with DNA. The conjugate, in turn, is formed by bonding receptor-specific ligands such as asialoglycoproteins to polycations such as polylysine through covalent bonds such as disulfide bonds. However, these preparations have not been applied to medical devices, nor were the asialoglyproteins modified to increase adsorption to medical devices.
A simple method of efficiently complexing nucleic acids, such as DNA, RNA and other nucleic acids, including anti-sense compositions and compositions including vectors, to surfaces of medical devices and other implantable devices would have wide applicability.
There remains a need in the art for coating compositions for implantable medical devices that include nucleic acids, and further wherein nucleic acid release can be modulated by the selection of appropriate reactants and components, and which can be applied simply and easily with no specialized equipment or techniques.
A primary object of the present invention is to provide a coating composition for contacting surfaces of implantable medical devices, wherein the composition comprises a heparin and nucleic acid condensate complex.
A further object of the invention is to provide an amphipathic silyl-heparin-nucleic acid condensate coating composition for contacting surfaces of implantable medical devices, which promotes sustained release of nucleic acids.
A further object of the present invention is to provide a cost effective and commercially feasible method for coating polymeric medical devices, including biodegradable medical devices, with a coating comprising nucleic acid condensate molecules.
A further object of the present invention is to provide a cost effective and commercially feasible method for coating polymeric medical devices, including biodegradable medical devices, with a coating comprising a silyl-heparin-nucleic acid condensate molecule composition.
A primary advantage of the present invention is that it provides for coating contacting surfaces of medical devices of complex geometries and surfaces with a durable and low-cost coating including nucleic acids that promotes the desired biological or therapeutic effect, depending on the nucleic acids selected.
Other objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.