Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Drug delivery
Reexamination Certificate
2000-03-20
2002-10-22
Thaler, Michael H. (Department: 3731)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Arterial prosthesis
Drug delivery
C604S891100, C623S901000
Reexamination Certificate
active
06468304
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an implant covered with a polymer capable of releasing various substances and, more particularly, to a stent covered with a polymer capable of encapsulating biologically active substances which are intended for the treatment of restenosis and of releasing them locally, and to a process for depositing a polymer on a support.
2. Description of the Related Art
Techniques have been developed in various medical fields which consist in introducing implants or prostheses into the human or animal body in order to correct or limit certain deficiencies.
Thus, in the field of cardiology, the technique of balloon angioplasty of arterial stenoses is widely used today in the treatment of coronary or peripheral vascular lesions responsible for angina pectoris, myocardial infarction and arteritis of the lower limbs. This technique consists in introducing, under angiographic control, a probe with an expandable balloon into the vessel to be treated at the contracted region and in reestablishing the blood flow by crushing the atheromatous plaque in the wall of the vessel. It is thus generally possible to avoid recourse to conventional surgical techniques in achieving arterial or peripheral revascularization.
However, angioplasty exhibits the disadvantage of often resulting in a further contraction of the artery, known as restenosis. In approximately 30 to 40% of cases, this restenosis occurs in a period of six months and cannot be predicted. It is essentially due to retractile healing of the artery and to proliferation of the smooth muscle cells of the arterial wall, in response to the attack produced by the introduction of the balloon. These two phenomena result in a further contraction of the arterial lumen.
The administration of medicaments, such as angiotensin converting enzyme inhibitors, anti-inflammatories, platelet anti-aggregants, anti-coagulants and the like, has not made it possible to effectively combat the phenomenon of restenosis.
Use is made, in preventing arterial retraction, of metallic endovascular prostheses in the form of a small spring, known as stents, which are inserted into the artery after having carried out the dilatation. The stent has the effect of impeding the immediate elastic return of the wall of the artery and, in the longer term, of preventing the constriction of the artery. On the other hand, the presence of the stent does not have a favorable effect on the proliferation of the smooth muscle cells and, in some cases, it can even aggravate it.
It is therefore desirable to be able to combine an effective medicinal treatment with the insertion of the stent.
It is known that some antisense oligonucleotides exert an in vitro and in vivo antiproliferative activity (M. R. Bennett et al., “Inhibition of vascular muscle cell accumulation in vitro and in vivo by c-myc antisense oligonucleotides”,
J. Clin. Invest. (
1994), 93, 820-28). However, no effective technique for the administration of such compounds has been described. Antisense nucleotide derivatives adsorbed or encapsulated in poly(alkyl cyanoacrylate) nanoparticles are disclosed in Patent FR-A-2,724,935, which provides this technique for their intratumoral administration in the treatment of certain cancers.
Patent DE-A-4,429,380 discloses a process for the preparation of stents with a ceramic or metallic support which are coated with an intermediate layer of amorphous silicon and with a layer of semiconductive material, these two layers overlapping each other.
Metallic stents covered with a first composite layer of a polymer and of a therapeutically active substance coated with a second layer of fibrin are disclosed in Patent Application EP-A-701,802. The polymer used is chosen from silicones, polyurethanes, polyesters, polyethers and vinyl derivatives. Furthermore, according to Patent EP-A-566,245, fibrin can be used in the treatment of restenosis. Tests carried out on pig coronary arteries with various biodegradable polymers (for example, polyglycolic acid/polylactic acid, polycaprolactone, and the like) or non-biodegradable polymers (polyurethane, silicone, poly(ethylene terephthalate)) have revealed significant inflammatory reactions accompanied by fibrocellular proliferation of the arterial wall (W. J. Van der Giessen et al.,
Circulation,
(1996), 94, 1690-97).
Thus, there currently exists no system effectively combining, in the treatment of restenosis, a stent and a substance having an antiproliferative effect on smooth muscle cells.
SUMMARY OF THE INVENTION
A subject-matter of the present invention is therefore a device which can be implanted in the body, or endoprosthesis, and in particular a stent, covered with a polymer capable of encapsulating biologically active substances with an anionic or cationic nature and of releasing them locally, which can be used in the treatment of various conditions and in particular of endoprosthetic thrombosis and of restenosis in the field of coronary angioplasty and of peripheral arterial angioplasty.
The invention also relates to a process which makes it possible to deposit an electrically conducting polymer, comprising a biologically active substance, on an electrically conducting support, such as a metallic support and in particular a stent.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The process in accordance with the present invention makes possible the electrochemical deposition of an electrically conducting polymer, for example a polymer derived from pyrrole, naphthalene or thiophene, which can be obtained in aqueous medium under mild conditions, that is to say at room temperature and under moderate saline conditions, from commercially available monomers. Furthermore, the electrochemical deposition makes possible precise control of the thickness of the polymer layer deposited on the support and the medium used does not comprise a chemical oxidizing agent or an organic solvent which might have harmful effects in the application envisaged. In the case where the electrochemical polymerization is difficult or cannot be envisaged, the polymer can be prepared in solution in an appropriate solvent, according to a conventional technique, and can be deposited on the support by spraying or dipping, followed by evaporation of the solvent.
The process of the invention comprises essentially two stages. In a first stage, an electropolymerization is carried out directly on the metallic support or, according to an alternative form, the polymer is prepared in solution and is deposited on the metallic support as indicated above. Then, in a second stage, an oxidation (if the polymer is cationic) or a reduction (if the polymer is anionic) is carried out and, simultaneously, the biologically active substance is attached to the polymer. The oxidation and the reduction, depending on the situation, are carried out electrochemically in a known way by creating a potential difference between the electrically conducting support and the polymer, in order to form respectively positive or negative charges which promote the attachment of the active substance. For example, the formation of a polymer matrix promotes the attachment of an active substance composed of a positively charged phosphorylated nucleic base; conversely, the formation of positive charges in the polymer promotes the attachment of an active substance composed, for example, of an oligonucleotide or a protein carrying negative sites, such as ATP, or more generally any negatively charged particle, such as heparin, a vector for plasmid genes or a linear or circular DNA fragment of plasmid type.
According to a preferred embodiment of the process of deposition of electrically conducting polymer in accordance with the invention, the electrochemical polymerization is carried out in the presence of a water-soluble polymer chosen from a polyethylene glycol, a polyvinylpyrrolidone, a polyethylene oxide, a copolymer of ethylene oxide and of propylene oxide of Poloxamer type, a polyethylene acetate, a poly(vinyl alcohol), a polyacrylamide and
Dubois-Rande Jean-Luc
Le Doan Trung
Pham Minh Chau
Piro Benoît
Teiger Emmanuel
Burns Doane Swecker & Mathis L.L.P.
Centre National de la Recherche Scientifique
Thaler Michael H.
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