1.ApplicationNumber: US-92179304-A
1.PublishNumber: US-2006039949-A1
2.Date Publish: 20060223
3.Inventor: NYCZ JEFFREY H.

4.Inventor Harmonized: NYCZ JEFFREY H(US)

5.Country: US
6.Claims:
(en)An acetabular cup having one or more osteoinductive formulations, wherein each osteoinductive formulation comprises one or more osteoinductive agent(s). In one embodiment of the invention, the acetabular cup comprises a porous coating into which the osteoinductive formulation is impregnated. In another embodiment of the invention, the acetabular cup comprises microchambers into which the osteoinductive formulation is sealed with a biodegradable or current responsive polymer. The osteoinductive formulations may be available in immediate or sustained release formulations. The invention further relates to preventing and treating osteolytic lesions formed following implantation of an acetabular cup during hip replacement surgery.

7.Description:
(en)FIELD OF THE INVENTION
The invention relates to an acetabular cup having one or more sustained release osteoinductive formulations, wherein the sustained release formulations comprise one or more osteoinductive agents. In one embodiment of the invention, the acetabular cup contains a plurality of microchambers, with each microchamber harboring a reservoir of osteoinductive formulation. In an alternative embodiment of the invention, the acetabular cup comprises a porous coating comprising an osteoinductive formulation impregnated within the porous coating of the acetabular cup. The osteoinductive formulations are available as immediate release or sustained release formulations.
BACKGROUND OF THE INVENTION
Thousands of implant surgeries are performed every year in the United States on patients requiring biomedical implants. Of the number of implants performed every year, a large number of implant surgeries are hip implant surgeries. For example, more than 168,000 total hip replacements are performed each year in the United States alone. Shindle, M., et al., BioMechanics, 11(2):22-32 (2004).
Unfortunately, implants introduced into patients during hip replacement surgeries are known to weaken or fail over time, often requiring revision surgery. The development of osteolytic lesions surrounding the biomedical implants used in hip replacements is known to play a role in the weakening or failure of biomedical devices used in hip replacements. Osteolysis is considered the dissolution of bone, particularly in the context of removal or loss of calcium of bone. In polyethylene implants requiring revision surgery, it is believed that polyethylene wear on adjacent bone tissue contributes to the development of osteolytic lesions.
One example of osteolysis is periprosthetic osteolyis. Using periprosthetic osteolysis as a model, recent studies have reported a 37% incidence of acetabular periprosthetic osteolysis and a 32% incidence of femoral osteolysis in patients receiving cemented sockets with an AML prosthesis; a 60% incidence of femoral periprosthetic osteolysis surrounding the HGP femoral component after 10 years, and 62% periprosthetic osteolysis in patients receiving the Omnifit/Dual Geometry combination of total hip replacements after 12 years. W. Harris, Clin. Orthopaed. Rel. Res., 393:66-70 (2001).
The incidence of periprosthetic osteolysis after a duration of 10 years is thought to exceed the incidence of sepsis, dislocation, fatal pulmonary embolization, nerve damage and other complications in patients receiving total hip replacements. W. Harris, p. 66 (2001). As can be seen, osteolysis is a prevalent condition that develops with hip replacements, and is known to play a role in the failure of hip replacements. The progression of osteolysis often results in the need for revision surgery, to replace worn implants and/or to re-seat implant components in endogenous bone.
The description herein of disadvantages and deleterious properties associated with known appartus, methods, compositions, and devices is not intended to limit the scope of the invention to their exclusion. Indeed, various embodiments of the invention may include one or more known appartus, methods, compositions, and devices without suffering from the disadvantages and deleterious properties described herein.
SUMMARY OF THE INVENTION
Accordingly, there remains a need in the art for biomedical implant devices that function in hip replacements, and which continue to maintain a high level of strength and utility over time. Furthermore, there remains a need in the art for biomedical implant devices that function in hip replacements that remain stable implants over time and in the presence of osteolysis.
Applicants describe herein preferred biomedical devices that fulfill the remaining need in the art for biomedical implant devices, useful in hip replacement surgeries, that continue to function while resisting the effects of osteolysis over time.
In accordance with a feature of an embodiment of the invention, there is provided an acetabular cup including an osteoinductive formulation. In accordance with an additional feature of an embodiment of the invention, there is provided a kit including an acetabular cup device for implantation and an osteoinductive formulation including an osteoinductive agent.
Another feature of an embodiment of the invention includes a method of of preventing or treating the development of osteolytic lesions in a hip implant patient comprising implanting in the patient an acetabular cup implant device including an osteoinductive formulation.
These and other features of embodiments of the invention will be readily apparent to those skilled in the art upon reading the detailed description that follows.


BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 provides an acetabular cup having discrete microchambers harboring reservoirs of osteoinductive formulation. In one embodiment of the invention, each osteoinductive formulation in the acetabular cup of FIG. 1 is a sustained release composition having a sustained release biodegradable polymer that biodegrades over time, releasing osteoinductive formulation.
FIG. 2 provides an acetabular cup having discrete microchambers harboring reservoirs of osteoinductive formulation. Each osteoinductive formulation in the acetabular cup of FIG. 2 is a sustained release composition that provides the osteoinductive formulation in bioavailable form over time in response to an electric current.
FIG. 3 provides an acetabular cup engineered with at least one electrode secured within the implant coating at the time of manufacture of the acetabular cup that functions to release osteoinductive formulations by applying an electric signal to the electrode


DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
For the purposes of promoting an understanding of the present invention, reference will now be made to preferred embodiments and specific language will be used to describe the same. The terminology used herein is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention. As used throughout this disclosure, the singular forms “a,” “an,” and “the” include plural reference unless the context clearly dictates otherwise. Thus, for example, a reference to “an acetabular cup” includes a plurality of such implants, as well as a single implant, and a reference to “an osteoinductive agent” is a reference to one or more agents and equivalents thereof known to those skilled in the art, and so forth.
Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods, devices, and materials are now described. All publications mentioned herein are cited for the purpose of describing and disclosing the various implants, osteoinductive agents, and other components that are reported in the publications and that might be used in connection with the invention. Nothing herein is to be construed as an admission that the invention is not entitled to antedate such disclosures by virtue of prior invention.
As used herein, “bioavailable” shall mean that the osteoinductive agents(s) are provided in vivo in the patient, wherein the osteoinductive agent(s) retain biological activity. By retaining biological activity is meant that the osteoinductive agent(s) retain at least 25% activity, more preferably at least 50% activity, still more preferably at least 75% activity, and most preferably at least 95% or more activity of the osteoinductive agent relative to the activity of the osteoinductive agent prior to implantation.
As used herein, “mature polypeptide” shall mean a post-translationally processed form of a polypeptide. For example, mature polypeptides may lack one or more of a signal peptide, prepropeptide and propeptide domains following expression in a host expression system. One of skill in the art of proteins is aware of the meanings of signal peptide, prepropeptide and propeptide domains.
As used herein, “electric potential or current” shall mean any electronic stimulus or current provided by a current producing apparatus, and traveling through conductive components to an electrode.
As used herein, “immediate release” shall mean formulations of the invention that provide the osteoinductive formulations in a reasonably immediate period of time.
As used herein, “sustained release” shall mean formulations of the invention that are designed to provide osteoinductive formulations at relatively consistent concentrations in bioavailable form over extended periods of time.
As used herein, “microchamber” shall mean a chamber with dimensions of about 2 mm depth by about 5 mm width, wherein the microchamber is capable of being asceptically sealed and is capable of containing osteoinductive formulations. In a preferred embodiment of the invention, the microchamber is cylindrical in shape.
As used herein, “biodegradable” shall mean a polymer that is degraded during in vivo application. In one embodiment of the invention, the degradation of the polymer produces the polymer monomeric subunits.
Acetabular cups for hip implantations are well known in the art, and generally speaking are exemplified by a cup having a cavity for receiving a femoral head, formed of a material having a predetermined tensile strength for implantation into a pelvic bone (See, e.g., U.S. Pat. Nos. 5,549,701; 5,609,648; and 5,879,398). The cup is typically secured to the patient's pelvic bone via bone screws, or alternatively is cemented in place. The outside diameter of the cup may vary depending on the size of the pelvic bone of the patient into which the acetabular cup prosthesis is to be implanted. The femoral head of a femoral implant is designed to reside and rotate within the cup implant, thereby replicating the natural actions of a human hip.
Decreasing the time necessary for the acetabular cup to become secure in the implantation site, or increasing the degree of stability of the acetabular cup implantation over extended periods of time, will increase the overall success of the hip replacement surgery. The present invention describes a novel acetabular cup useful with hip implantations that at least increases the stability of the acetabular cup implant in a hip replacement.
In one embodiment of the invention shown in FIG. 1 , the acetabular cup allows for the incorporation of discrete microchambers harboring osteoinductive formulations. The acetabular cup preferably includes a plurality of microchambers [ 14 ] harboring reservoirs of osteoinductive formulation [ 16 ] comprising one or more osteoinductive agents. The acetabular cup [ 10 ] optionally comprises one or more biodegradable or current responsive polymer compositions in the form of polymeric plug(s) or polymer coatings [ 12 ] that seal the osteoinductive formulation within the microchamber [ 14 ] present in the base material of the acetabular cup [ 10 ], as displayed in FIG. 1 . In one embodiment of the invention, the polymeric plugs or polymer coatings include osteoinductive formulations comprising one or more osteoinductive agent(s). The polymeric plugs or polymer coatings preferably are biodegradable or current responsive polymers that degrade, denature or otherwise release the contents of the microchambers following degradation of the polymer plugs or polymer coatings, or alternatively following the application of electric potential or current to the polymer plugs or polymer coatings.
The osteoinductive formulations may be provided in the microchambers present in the acetabular cup and aseptically sealed in the plurality of microchambers with biodegradable or current responsive polymers. The biodegradable polymers may comprise a polymeric formulation resulting in the release of the osteoinductive formulations at about the same time based on biodegradation rates of the polymer. Alternatively, the plurality of microchambers may comprise polymeric formulations having different degradation profiles and resulting in the release of the osteoinductive formulations at differing times or rates of release, again based on differing biodegradation rates of the polymer used to seal the microchambers harboring osteoinductive formulations.
In another embodiment of the invention, the osteoinductive formulation provides osteoinductive agent(s) in bioavailable form as sustained release compositions. The sustained release polymeric formulations comprise a biodegradable polymer that releases osteoinductive formulations comprising osteoinductive agent(s) in a time-wise manner based on the rate of degradation of the biodegradable polymer plug and/or a biodegradable polymer composition into which the osteoinductive formulation was included.
In a further embodiment of the invention, the osteoinductive formulation provides osteoinductive agent(s) in bioavailable form from sustained release formulations due to the application of an electric potential or current to a current responsive polymer that seals the microchamber. As shown in FIG. 2 , the osteoinductive formulations are sealed in the microchamber by a current responsive polymer [ 110 ] that releases osteoinductive formulations comprising osteoinductive agent(s) in response to the induction of an electric current in an electrode [ 120 ] embedded within the current responsive polymer [ 110 ]. The electrode is positioned in the polymeric plug in a manner that degrades the polymer surrounding the electrode following the induction of the electric current, thus liberating the osteoinductive formulation [ 130 ] comprising the osteoinductive agent(s) in bioavailable form from the microchamber [ 140 ]. The osteoinductive formulation is released from the microchamber via diffusion and endogenous fluid forces applied against the microchamber following application of the electric potential or current to the current responsive polymer. The electrode is conductively coupled to an implantable current-providing device. In one embodiment of the invention, the implantable current-providing device is programmable such that the release of osteoinductive formulations from the plurality of microchambers can be programmed in sequence, in time, or both. A programmable current inducing device (e.g., a voltage supply or current supply) preferably contains one or more of the following components, optionally including all of the listed components: a signal receiver or biosensor and a microprocessor adapted to process signals from the signal receiver or biosensor in order to induce a current in the electrode [ 120 ]. Preferably the current inducing device is small and capable of providing sufficient power for extended durations of time, such as for example, by using lithium batteries. In this embodiment of the invention, the acetabular cup orthopaedic device comprises a plurality of microchambers, each with a current-responsive polymer seal comprising an electrode that is conductively coupled to an implantable current inducing device.
In another embodiment of the invention, an acetabular cup is provided that comprises a porous coating that is impregnated with an osteoinductive formulation. The porous coating may be an integral component of the base material of the acetabular cup, or alternatively may be a secondary coating that is applied over the base material of the acetabular cup. The osteoinductive formulation impregnated into the porous coating may be an immediate release formulation, or alternatively may be a sustained release formulation. The porous coating of the acetabular cup is impregnated with the preferred osteoinductive formulation (immediate release or sustained release) at the time of production of the acetabular cup, or alternatively, prior to implantation.
In a non-limiting hypothesis of the manner in which the acetabular cup will increase the overall success of the hip replacement surgery, the one or more osteoinductive agents present in the osteoinductive formulation promote the in-growth of endogenous bone tissue into the acetabular cup, thereby increasing the degree to which the acetabular cup is secured in the pelvic bone. In another non-limiting hypothesis of the manner in which the acetabular cup will increase the overall success of the hip replacement surgery, the acetabular cup decreases the amount of osteolysis that occurs over time because the endogenous bone ingrowth induced by the osteoinductive agent(s) allows the acetabular cup to become osteointegrated and relatively resistant to the fluids and particulate debris believed to contribute to the development of osteolysis.
In another embodiment of the invention, the acetabular cup of the invention further utilizes bone screws or bone cement as a means of initial fixation of enhanced fixation to the site of implantation, in conjunction with the osteoinductive formulations and microchambers described supra.
Another aspect of the invention relates to osteoinductive formulations useful with the acetabular cup of the invention. Osteoinductive formulations comprise one or more osteoinductive agents, and provide the one or more agents in bioavailable form as immediate release or sustained release formulations. Osteoinductive formulations further optionally comprise one or more of the following components: antibiotics, carriers, bone marrow aspirate, bone marrow concentrate, demineralized bone matrix, immunosuppressives, agents that enhance isotonicity and chemical stability, and any combination of one or more, including all, of the recited components.
The osteoinductive formulations of the invention comprise one or more osteoinductive agent(s) that are provided to induce growth of endogenous bone, or tissues related to the endogenous bone such as connective tissues and vascular tissues. Additionally, the osteoinductive agents are provided to inhibit bone resorption. The osteoinductive formulations comprise osteoinductive agents, such as for example, one or more Bone Morphogenetic Protein (BMP), one or more Connective Tissue Growth Factor (CTGF), one or more Vascular Endothelial Growth Factor (VEGF), Osteoprotegerin (OPG), Periostin and one or more Tissue Growth Factor-beta (TGF-β) polynucleotides and polypeptides. In one embodiment of the invention, the osteoinductive agent is provided in bioavailable form from sustained release biodegradable polymers or microchambers sealed with biodegradable polymers due to degradation of biodegradeable polymers retaining the osteoinductive formulation. In another embodiment of the invention, osteoinductive agent is provided in bioavailable form from the microchamber in response to application of an electric potential or current.
The osteoinductive formulations of the invention are available as immediate release formulations or sustained release formulations. One of skill in the art of implant surgery is able to determine whether a patient would benefit from immediate release formulations or sustained release formulations based on factors such as age and level of physical activity. Therefore, the osteoinductive formulations of the invention are available as immediate or sustained release formulations.
Representative immediate release formulations are liquid formulations comprising at least osteoinductive agent(s) that are introduced into the acetabular cup, and remain available in liquid form in vivo. The liquid formulations provide osteoinductive agent in bioavailable form at rates that are dictated by the fluid properties of the liquid formulation, such as diffusion rates at the site of implantation, the influence of endogenous fluids, etc. Examples of suitable liquid formulations comprise water, saline, or other acceptable fluid mediums that will not induce host immune responses.
Immediate release formulations of the invention provide the osteoinductive formulation in a reasonably immediate period of time, although factors such as proximity to bodily fluids, density of application of the formulations, etc, will influence the period of time within which the osteoinductive agent is liberated from the formulation. However, immediate release formulations are not designed to retain the one or more osteoinductive agents for extended periods of time, and typically will lack a biodegradable polymer, except where the biodegradable polymer is used as the component that seals the plurality of microchambers harboring immediate release osteoinductive formulation.
In another embodiment of the invention, osteoinductive formulations are available in sustained release formulations that provide the osteoinductive formulation(s) in bioavailable form over extended periods of time. The duration of release from the sustained release formulations is dictated by the nature of the formulation and other factors discussed supra, such as for example proximity to bodily fluids and density of application of the formulations, as well as the degradation rates of biodegradeable polymers comprising the osteoinductive formulations. However, sustained release formulations are designed to provide osteoinductive agents in the formulations at relatively consistent concentrations in bioavailable form over extended periods of time. Biodegradable sustained release polymers useful with the osteoinductive formulations are well known in the art and include, but are not limited to, polylactides, polyglycolides, polycaprolactones, polyanhydrides, polyamides, polyurethanes, polyesteramides, polyorthoesters, polydioxanones, polyacetals, polyketals, polycarbonates, polyorthocarbonates, polyphosphazenes, polyhydroxybutyrates, polyhydroxyvalerates, polyalkylene oxalates, polyalkylene succinates, poly(malic acid), poly(amino acids), polyvinylpyrrolidone, polyethylene glycol, polyhydroxycellulose, chitin, chitosan, poly(L-lactic acid), poly(lactide-co-glycolide), poly(hydroxybutyrate-co-valerate), and copolymers, terpolymers, or combinations or mixtures of the above materials. The release profile of the biodegradable polymer can further be modified by inclusion of biostable polymers that influence the biodegradation rate of the polymer composition. Biostable polymers that could be incorporated into the biodegradable polymers, thereby influencing the rates of biodegradation, include but are not limited to silicones, polyesters, vinyl homopolymers and copolymers, acrylate homopolymers and copolymers, polyethers, and cellulosics.
The biodegradable polymers can be solid form polymers or alternatively can be liquid polymers that solidify in a reasonable time after application. Suitable liquid polymers formulations include, but are not limited to those polymer compositions disclosed in, for example, U.S. Pat. Nos. 5,744,153, 4,938,763, 5,278,201 and 5,278,202, the contents of each of which are herein incorporated by reference in their entireties. These patents disclose liquid polymer compositions that are useful as controlled drug-release compositions or as implants. The liquid prepolymer has at least one polymerizable ethylenically unsaturated group (e.g., an acrylic-ester-terminated prepolymer). If a curing agent is employed, the curing agent is typically added to the composition just prior to use. The prepolymer remains a liquid for a short period of time after the introduction of the curing agent. During this period of time the liquid delivery composition may be introduced into the acetabular cup, e.g., via syringe. The mixture then solidifies to form a solid composition. The liquid polymer compositions may be administered to a patient in liquid form, and will then solidify or cure at the site of introduction to form a solid polymer composition. Biodegradable forms of the polymers are contemplated, and mixtures of biodegradable and biostable polymers that affect the rate of biodegradation of the polymer are further contemplated.
Osteoinductive formulations of the invention further contemplate the use of aqueous and non-aqueous peptide formulations that maintain stability of the osteoinductive agents over extended periods of time. Non-limiting examples of aqueous and non-aqueous formulations useful for the long-term stability of osteoinductive agent(s) include those formulations provided in U.S. Pat. Nos. 5,916,582; 5,932,547, and 5,981,489, the disclosures of each of which are herein incorporated by reference.
As noted supra, in one embodiment of the invention the osteoinductive formulations are impregnated in a porous coating substrate on the acetabular cup. An amount of the liquid composition is dispensed into the porous substrate, such as by spraying, painting or squirting, and the liquid formulation solidifies following administration to provide a sustained release formulation.
In another embodiment of the invention, the liquid compositions which are useful for the delivery of osteoinductive formulations in vivo include conjugates of the osteoinductive agent with a water-insoluble biocompatible polymer, with the dissolution of the resultant polymer-active agent conjugate in a biocompatible solvent to form a liquid polymer system. In addition, the liquid polymer system may also include a water-insoluble biocompatible polymer which is not conjugated to the osteoinductive agent. In one embodiment of the invention, these liquid compositions may be introduced into the body of a subject in liquid form. The liquid composition then solidifies or coagulates in situ to form a controlled release implant where the osteoinductive agent is conjugated to the solid matrix polymer.
Osteoinductive agents are discussed infra. Osteoinductive agents of the invention are administered in the osteoinductive formulations as polypeptides or polynucleotides. Polynucleotide compositions of the isolated osteoinductive agents include, but are not limited to, isolated Bone Morphogenetic Protein (BMP), Vascular Endothelial Growth Factor (VEGF), Connective Tissue Growth Factor (CTGF), Osteoprotegerin, Periostin and Transforming Growth Factor beta (TGF-β) polynucleotides. Polynucleotide compositions of the osteoinductive agents include, but are not limited to, gene therapy vectors harboring polynucleotides encoding the osteoinductive polypeptides of interest. Gene therapy methods require a polynucleotide which codes for the osteoinductive polypeptide operatively linked or associated to a promoter and any other genetic elements necessary for the expression of the osteoinductive polypeptide by the target tissue. Such gene therapy and delivery techniques are known in the art, See, for example, International Publication No. WO90/11092, which is herein incorporated by reference. Suitable gene therapy vectors include, but are not limited to, gene therapy vectors that do not integrate into the host genome. Alternatively, suitable gene therapy vectors include, but are not limited to, gene therapy vectors that integrate into the host genome.
In one embodiment, the polynucleotide of the invention is delivered in plasmid formulations. Plasmid DNA or RNA formulations refer to sequences encoding osteoinductive polypeptides that are free from any delivery vehicle that acts to assist, promote or facilitate entry into the cell, including viral sequences, viral particles, liposome formulations, lipofectin or precipitating agents and the like. Optionally, gene therapy compositions of the invention can be delivered in liposome formulations and lipofectin formulations, which can be prepared by methods well known to those skilled in the art. General methods are described, for example, in U.S. Pat. Nos. 5,593,972, 5,589,466, and 5,580,859, which are herein incorporated by reference.
Gene therapy vectors further comprise suitable adenoviral vectors including, but not limited to for example, those described in Kozarsky and Wilson, Curr. Opin. Genet. Devel., 3:499-503 (1993); Rosenfeld et al., Cell, 68:143-155 (1992); Engelhardt et al., Human Genet. Ther., 4:759-769 (1993); Yang et al., Nature Genet., 7:362-369 (1994); Wilson et al., Nature, 365:691-692 (1993); and U.S. Pat. No. 5,652,224, which are herein incorporated by reference.
Polypeptide compositions of the isolated osteoinductive agents include, but are not limited to, isolated Bone Morphogenetic Protein (BMP), Vascular Endothelial Growth Factor (VEGF), Connective Tissue Growth Factor (CTGF), Osteoprotegerin, Periostin and Transforming Growth Factor beta (TGF-β) polypeptides. Polypeptide compositions of the osteoinductive agents include, but are not limited to, full length proteins, fragments and variants thereof. In a preferred embodiment of the invention, polypeptide fragments of the osteoinductive agents are propeptide forms of the isolated full length polypeptides. In a particularly preferred embodiment of the invention, polypeptide fragments of the osteoinductive agents are mature forms of the isolated full length polypeptides. Also preferred are the polynucleotides encoding the propeptide and mature polypeptides of the osteoinductive agents.
Variants of the osteoinductive agents of the invention include, but are not limited to, protein variants that are designed to increase the duration of activity of the osteoinductive agent in vivo. Preferred embodiments of variant osteoinductive agents include, but are not limited to, full length proteins or fragments thereof that are conjugated to polyethylene glycol (PEG) moieties to increase their half-life in vivo (also known as pegylation). Methods of pegylating polypeptides are well known in the art (See, e.g., U.S. Pat. No. 6,552,170 and European Patent No. 0,401,384 as examples of methods of generating pegylated polypeptides).
In another embodiment of the invention, the osteoinductive agent(s) are provided in the osteoinductive formulation(s) as fusion proteins. In one embodiment, the osteoinductive agent(s) are available as fusion proteins with the Fc portion of human IgG. In another embodiment of the invention, the osteoinductive agent(s) of the invention are available as hetero- or homodimers or multimers. Examples of preferred fusion proteins include, but are not limited to, ligand fusions between mature osteoinductive polypeptides and the Fc portion of human Immunoglobulin G (IgG). Methods of making fusion proteins and constructs encoding the same are well known in the art.
Osteoinductive agents of the invention that are included with the osteoinductive formulations are sterile. In a non-limiting method, sterility is readily accomplished for example by filtration through sterile filtration membranes (e.g., 0.2 micron membranes or filters).
In one embodiment of the invention, the acetabular cup is packaged without impregnated osteoinductive formulations, such as for example where the acetabular cup comprises a porous substrate into which the osteoinductive formulations of the invention are subsequently impregnated. In such a situation, osteoinductive agents generally are placed into a container having a sterile access port, for example, an intravenous solution bag or vial having a stopper pierceable by a hypodermic injection needle. In one embodiment, osteoinductive agents and prepared osteoinductive formulations are stored in separate containers, for example, sealed ampoules or vials, as an aqueous solution or as a lyophilized formulation for reconstitution. As an example of a lyophilized formulation, 10-ml vials are filled with 5 ml of sterile-filtered 1% (w/v) aqueous osteoinductive agent solution, and the resulting mixture is lyophilized. The osteoinductive agent is prepared by reconstituting the lyophilized agent prior to administration in an appropriate solution, admixed with the prepared osteoinductive formulations and administered to the acetabular cup prior to or concurrent with implantation into a patient.
As one of skill in the art will recognize, the concentrations of osteoinductive agent can be variable based on the desired length or degree of osteoinduction. Similarly, one of skill in the art will understand that the duration of sustained release can be modified by the manipulation of the compositions comprising the sustained release formulation, such as for example, modifying the percent of biostable polymers found within a sustained release formulation.
Another method to provide liquid compositions which are useful for the delivery of osteoinductive agents in vivo and permit the initial burst of active agent to be controlled more effectively than previously possible is to conjugate the active agent with a water-insoluble biocompatible polymer and dissolve the resultant polymer-active agent conjugate in a biocompatible solvent to form a liquid polymer system similar to that described in U.S. Pat. Nos. 4,938,763, 5,278,201 and 5,278,202. The water-insoluble biocompatible polymers may be those described in the above patents or related copolymers. In addition, the liquid polymer system may also include a water-insoluble biocompatible polymer which is not conjugated to the active agent. In one embodiment of the invention, these liquid compositions may be introduced into the body of a subject in liquid form. The liquid composition then solidifies or coagulates in situ to form a controlled release implant where the active agent is conjugated to the solid matrix polymer.
The formulation employed to form the controlled release implant in situ may be a liquid delivery composition which includes a biocompatible polymer which is substantially insoluble in aqueous medium, an organic solvent which is miscible or dispersible in aqueous medium, and the controlled release component. The biocompatible polymer is substantially dissolved in the organic solvent. The controlled release component may be either dissolved, dispersed or entrained in the polymer/solvent solution. In a preferred embodiment, the biocompatible polymer is biodegradable and/or bioerodable. The liquid polymer formulation is delivered to the decompression core using instruments well known in the art, for example, canulas capable of delivering liquid formulations.
Osteoinductive formulations of the invention optionally further comprise de-mineralized bone matrix compositions (hereinafter “DBM” compositions), bone marrow aspirate, bone marrow concentrate, or combinations or permutations of any of the same. Methods for producing DBM are well known in the art, and DBM may be obtained following the teachings of O'Leary et al (U.S. Pat. No. 5,073,373) or by obtaining commercially available DBM formulations such as, for example, AlloGro® available from suppliers such as AlloSource® (Centennial, Colo.). Methods of obtaining bone marrow aspirates as well as devices facilitating extraction of bone marrow aspirate are well known in the art and are described, for example, by Turkel et al in U.S. Pat. No. 5,257,632.
Osteoinductive formulations of the invention optionally further comprise antibiotics that are administered with the osteoinductive agent. As discussed by Vehmeyer et al., the possibility exists that bacterial contamination can occur for example due to the introduction of contaminated allograft tissue from living donors. Vehmeyer, S B, et al., Acta Orthop Scand., 73(2): 165-169 (2002). Antibiotics of the invention are also co-administered with the osteoinductive formulations to prevent infection by obligate or opportunistic pathogens that are introduced to the patient during implant surgery.
Antibiotics useful with the osteoinductive formulations of the invention include, but are not limited to, amoxicillin, beta-lactamases, aminoglycosides, beta-lactam (glycopeptide), clindamycin, chloramphenicol, cephalosporins, ciprofloxacin, erythromycin, fluoroquinolones, macrolides, metronidazole, penicillins, quinolones, rapamycin, rifampin, streptomycin, sulfonamide, tetracyclines, trimethoprim, trimethoprim-sulfamthoxazole, and vancomycin. In addition, one skilled in the art of implant surgery or administrators of locations in which implant surgery occurs may prefer the introduction of one or more the above-recited antibiotics to account for nosocomial infections or other factors specific to the location where the surgery is conducted. Accordingly, the osteoinductive formulations of the invention contemplate that one or more of the antibiotics recited supra, and any combination of one or more of the same antibiotics, may be included in the osteoinductive formulations of the invention.
The osteoinductive formulations of the invention optionally further comprise immunosuppressive agents, particularly in circumstances where allograft compositions are administered to the patient. Suitable immunosuppressive agents that may be administered in combination with the osteoinductive formulations of the invention include, but are not limited to, steroids, cyclosporine, cyclosporine analogs, cyclophosphamide, methylprednisone, prednisone, azathioprine, FK-506, 15-deoxyspergualin, and other immunosuppressive agents that act by suppressing the function of responding T cells. Other immunosuppressive agents that may be administered in combination with the osteoinductive formulations of the invention include, but are not limited to, prednisolone, methotrexate, thalidomide, methoxsalen, rapamycin, leflunomide, mizoribine (bredinin™), brequinar, deoxyspergualin, and azaspirane (SKF 105685), Orthoclone OKT™ 3 (muromonab-CD3). Sandimmune™, Neoral™, Sangdya™ (cyclosporine), Prograf™ (FK506, tacrolimus), Cellcept™ (mycophenolate motefil, of which the active metabolite is mycophenolic acid), Imuran™ (azathioprine), glucocorticosteroids, adrenocortical steroids such as Deltasone™ (prednisone) and Hydeltrasol™ (prednisolone), Folex™ and Mexate™ (methotrexate), Oxsoralen-Ultra™ (methoxsalen) and Rapamuen™ (sirolimus).
Osteoinductive formulations of the invention may optionally further comprise a carrier vehicle such as water, saline, Ringer's solution, calcium phosphate based carriers, or dextrose solution. Non-aqueous vehicles such as fixed oils and ethyl oleate are also useful herein, as well as liposomes.
In one embodiment of the invention, collagen is used as a carrier for the osteoinductive formulations. In another embodiment of the invention, collagen in combination with glycosaminoglycan is utilized as a carrier for the osteoinductive formulations, as described in U.S. Pat. No. 5,922,356, which is herein incorporated by reference. The content of glycosaminoglycan in the formulation is preferably less than 40% by weight of the formulation, more preferably 1-10%. Collagen is preferably 20-95% by weight of the formulation, more preferably 40-60 (wt/wt)%.
Any collagen may be used as a carrier for osteoinductive formulations. Examples of suitable collagen to be used as a carrier include, but are not limited to, human collagen type I, human collagen type II, human collagen type III, human collagen type IV, human collagen type V, human collagen type VI, human collagen type VII, human collagen type VIII, human collagen type IX, human collagen type X, human collagen type XI, human collagen type XII, human collagen type XIII, human collagen type XIV, human collagen type XV, human collagen type XVI, human collagen type XVII, human collagen type XVIII, human collagen type XIX, human collagen type XXI, human collagen type XXII, human collagen type XXIII, human collagen type XXIV, human collagen type XXV, human collagen type XXVI, human collagen type XXVII, and human collagen type XXVIII, and combinations thereof. Collagen carriers useful with the invention further comprise, or alternatively consist of, hetero- and homo-trimers of any of the above-recited collagen types. In a preferred embodiment of the invention, collagen carriers comprise, or alternatively consist of, hetero- or homo-trimers of human collagen type I, human collagen type II, and human collagen type III, or combinations thereof.
The collagen utilized as a carrier may be human or non-human, as well as recombinant or non-recombinant. In a preferred embodiment of the invention, the collagen utilized as a carrier is recombinant collagen. Methods of making recombinant collagen are known in the art, for example, by using recombinant methods such as those methods described in U.S. Pat. No. 5,895,833 (trangenic production), J. Myllyharju, et al., Biotechnology of Extracellular Matrix, 353-357 (2000) (production of recombinant human types I-III in Pichia pastoris ), Wong Po Foo, C., et al., Adv. Drug Del. Rev., 54:1131-1143 (2002), or by Toman, P. D., et al., J. Biol. Chem., 275(30):23303-23309 (2001), the disclosures of each of which are herein incorporated by reference. Alternatively, recombinant human collagen types are obtained from commercially available sources, such as for example, as provided by FibroGen (San Francisco, Calif.).
The osteoinductive formulations of the invention further optionally include substances that enhance isotonicity and chemical stability. Such materials are non-toxic to patients at the dosages and concentrations employed, and include buffers such as phosphate, citrate, succinate, acetic acid, and other organic acids or their salts; antioxidants such as ascorbic acid; low molecular weight (less than about ten residues) polypeptides, e.g., polyarginine or tripeptides; proteins, such as serum albumin, gelatin, or immunoglobulins; amino acids, such as glycine, glutamic acid, aspartic acid, or arginine; monosaccharides, disaccharides, and other carbohydrates including cellulose or its derivatives, glucose, mannose, or dextrins; chelating agents such as EDTA; sugaralcohols such as mannitol or sorbitol; counterions such as sodium; and/or nonionicsurfactants such as polysorbates, poloxamers, or PEG.
Osteoinductive formulations of the invention further comprise isolated osteoinductive agents. Isolated osteoinductive agents of the invention promote the in-growth of endogenous bone into the acetabular cup, or aid in preventing resorption of bone tissue surrounding the acetabular cup implant by osteoclasts. Isolated osteoinductive agents of the invention are available as polypeptides or polynucleotides. Isolated osteoinductive agents of the invention comprise full length proteins and fragments thereof, as well as polypeptide variants or mutants of the isolated osteoinductive agents provided herein.
In another embodiment of the invention, osteoinductive agent polypeptides are available as heterodimers or homodimers, as well as multimers or combinations thereof.
Recombinantly expressed proteins may be in native forms, truncated analogs, muteins, fusion proteins, and other constructed forms capable of inducing bone, cartilage, or other types of tissue formation as demonstrated by in vitro and ex vivo bioassays and in vivo implantation in mammals, including humans.
The invention further contemplates the use of polynucleotides and polypeptides having at least 95% homology, more preferably 97%, and even more preferably 99% homology to the isolated osteoinductive agent polynucleotides and polypeptides provided herein. Typical osteoinductive formulations comprise isolated osteoinductive agent at concentrations of from about 0.1 mg/ml to 100 mg/ml, preferably 1-10 mg/ml, at a pH of about 3 to 8.
In one embodiment of the invention, isolated osteoinductive agents include one or more polynucleotides or polypeptides of members of the family of Bone Morphogenetic Proteins (“BMPs”). BMPs are a class of proteins thought to have osteoinductive or growth-promoting activities on endogenous bone tissue. Known members of the BMP family include, but are not limited to, BMP-1, BMP-2, BMP-3, BMP-4, BMP-5, BMP-6, BMP-7, BMP-8, BMP-9, BMP-10, BMP-11, BMP-12, BMP-13, BMP-15, BMP-16, BMP-17, and BMP-18.
BMPs useful as isolated osteoinductive agents include, but are not limited to, the following BMPs:
BMP-1 polynucleotides and polypeptides corresponding to SEQ iD NO:1, SEQ ID NO:2, SEQ ID NO:3 and SEQ ID NO:4, as well as mature BMP-1 polypeptides and polynucleotides encoding the same; BMP-2 polynucleotides and polypeptides corresponding to SEQ ID NO:5 and SEQ ID NO:6, as well as mature BMP-2 polypeptides and polynucleotides encoding the same; BMP-3 polynucleotides and polypeptides corresponding to SEQ ID NO:7 and SEQ ID NO:8, as well as mature BMP-3 polypeptides and polynucleotides encoding the same; BMP-4 polynucleotides and polypeptides corresponding to SEQ ID NO:9 and SEQ ID NO:10, as well as mature BMP-4 polypeptides and polynucleotides encoding the same; BMP-5 polynucleotides and polypeptides corresponding to SEQ ID NO:11, SEQ ID NO:12, SEQ ID NO:13 and SEQ ID NO:14, as well as mature BMP-5 polypeptides and polynucleotides encoding the same; BMP-6 polynucleotides and polypeptides corresponding to SEQ ID NO:15, SEQ ID NO:16, SEQ ID NO:17 and SEQ ID NO:18, as well as mature BMP-6 polypeptides and polynucleotides encoding the same; BMP-7 polynucleotides and polypeptides corresponding to SEQ ID NO:19, SEQ ID NO:20, SEQ iD NO:21 and SEQ ID NO:22, as well as mature BMP-7 polypeptides and polynucleotides encoding the same; BMP-8 polynucleotides and polypeptides corresponding to SEQ ID NO:23, SEQ ID NO:24, SEQ ID NO:25 and SEQ ID NO:26, as well as mature BMP-8 polypeptides and polynucleotides encoding the same; BMP-9 polynucleotides and polypeptides corresponding to SEQ ID NO:27 and SEQ ID NO:28, as well as mature BMP-9 polypeptides and polynucleotides encoding the same; BMP-10 polynucleotides and polypeptides corresponding to SEQ ID NO:29, SEQ ID NO:30, SEQ ID NO:31 and SEQ ID NO:32, as well as mature BMP-10 polypeptides and polynucleotides encoding the same; BMP-11 polynucleotides and polypeptides corresponding to SEQ ID NO:33 and SEQ ID NO:34, as well as mature BMP-1 polypeptides and polynucleotides encoding the same; BMP-12 polynucleotides and polypeptides corresponding to SEQ ID NO:35 and SEQ ID NO:36, as well as mature BMP-12 polypeptides and polynucleotides encoding the same; BMP-13 polynucleotides and polypeptides corresponding to SEQ ID NO:37 and SEQ ID NO:38, as well as mature BMP-13 polypeptides and polynucleotides encoding the same; BMP-15 polynucleotides and polypeptides corresponding to SEQ ID NO: 39, SEQ ID NO:40, SEQ ID NO:41 and SEQ ID NO:42, as well as mature BMP-15 polypeptides and polynucleotides encoding the same; BMP-16 polynucleotides and polypeptides corresponding to SEQ ID NO:43, SEQ ID NO:44, SEQ ID NO:45 and SEQ ID NO:46, as well as mature BMP-16 polypeptides and polynucleotides encoding the same; BMP-17 polynucleotides and polypeptides corresponding to SEQ ID NO:47 and SEQ ID NO:48, as well as mature BMP-17 polypeptides and polynucleotides encoding the same; and BMP-18 polynucleotides and polypeptides corresponding to SEQ ID NO:49 and SEQ ID NO:50, as well as mature BMP-18 polypeptides and polynucleotides encoding the same.

BMPs utilized as osteoinductive agents of the invention comprise, or alternatively consist of, one or more of BMP-1; BMP-2; BMP-3; BMP-4; BMP-5; BMP-6; BMP-7; BMP-8; BMP-9; BMP-10; BMP-11; BMP-12; BMP-13; BMP-15; BMP-16; BMP-17; and BMP-18; as well as any combination of one or more of these BMPs, including full length BMPs or fragments thereof, or combinations thereof, either as polypeptides or polynucleotides encoding said polypeptide fragments of all of the recited BMPs. The isolated BMP osteoinductive agents may be administered as polynucleotides, polypeptides, or combinations of both.
In a particularly preferred embodiment of the invention, isolated osteoinductive agents comprise, or alternatively consist of, BMP-2 polynucleotides or polypeptides or mature fragments of the same.
In another embodiment of the invention, isolated osteoinductive agents include osteoclastogenesis inhibitors to inhibit bone resorption of the bone tissue surrounding the site of implantation of the acetabular cup by osteoclasts.
Osteoclast and Osteoclastogenesis inhibitors include, but are not limited to, Osteoprotegerin polynucleotides and polypeptides corresponding to SEQ ID NO:51, SEQ ID NO:52, SEQ ID NO:53 and SEQ ID NO:54, as well as mature Osteoprotegerin polypeptides and polynucleotides encoding the same. Osteoprotegerin is a member of the TNF-receptor superfamily and is an osteoblast-secreted decoy receptor that functions as a negative regulator of bone resorption. This protein specifically binds to its ligand, osteoprotegerin ligand (TNFSF11/OPGL), both of which are key extracellular regulators of osteoclast development.
Osteoclastogenesis inhibitors further include, but are not limited to, chemical compounds such as bisphosphonate, 5-lipoxygenase inhibitors such as those described in U.S. Pat. Nos. 5,534,524 and 6,455,541 (the contents of which are herein incorporated by reference), heterocyclic compounds such as those described in U.S. Pat. No. 5,658,935 (herein incorporated by reference), 2,4-dioxoimidazolidine and imidazolidine derivative compounds such as those described in U.S. Pat. Nos. 5,397,796 and 5,554,594 (the contents of which are herein incorporated by reference), sulfonamide derivatives such as those described in U.S. Pat. No. 6,313,119 (herein incorporated by reference), and acylguanidine compounds such as those described in U.S. Pat. No. 6,492,356 (herein incorporated by reference).
In another embodiment of the invention, isolated osteoinductive agents include one or more polynucleotides or polypeptides of members of the family of Connective Tissue Growth Factors (“CTGFs”). CTGFs are a class of proteins thought to have growth-promoting activities on connective tissues. Known members of the CTGF family include, but are not limited to, CTGF-1, CTGF-2, and CTGF-4.
CTGFs useful as isolated osteoinductive agents include, but are not limited to, the following CTGFs:
CTGF-1 polynucleotides and polypeptides corresponding to SEQ ID NO:55, SEQ ID NO:56, SEQ ID NO:57 and SEQ ID NO:58, as well as mature CTGF-1 polypeptides and polynucleotides encoding the same.
CTGF-2 polynucleotides and polypeptides corresponding to SEQ ID NO:59 and SEQ ID NO:60, as well as mature CTGF-2 polypeptides and polynucleotides encoding the same.
CTGF-4 polynucleotides and polypeptides corresponding to SEQ ID NO:61 and SEQ ID NO:62, as well as mature CTGF-4 polypeptides and polynucleotides encoding the same.
In another embodiment of the invention, isolated osteoinductive agents include one or more polynucleotides or polypeptides of members of the family of Vascular Endothelial Growth Factors (“VEGFs”). VEGFs are a class of proteins thought to have growth-promoting activities on vascular tissues. Known members of the VEGF family include, but are not limited to, VEGF-A, VEGF-B, VEGF-C, VEGF-D and VEGF-E.
VEGFs useful as isolated osteoinductive agents include, but are not limited to, the following VEGFs:
VEGF-A polynucleotides and polypeptides corresponding to SEQ ID NO:63 and SEQ ID NO:64, as well as mature VEGF-A polypeptides and polynucleotides encoding the same.
VEGF-B polynucleotides and polypeptides corresponding to SEQ ID NO:65 and SEQ ID NO:66, as well as mature VEGF-B polypeptides and polynucleotides encoding the same.
VEGF-C polynucleotides and polypeptides corresponding to SEQ ID NO:67 and SEQ ID NO:68, as well as mature VEGF-C polypeptides and polynucleotides encoding the same.
VEGF-D polynucleotides and polypeptides corresponding to SEQ ID NO:69 and SEQ ID NO:70, as well as mature VEGF-D polypeptides and polynucleotides encoding the same.
VEGF-E polynucleotides and polypeptides corresponding to SEQ ID NO:71 and SEQ ID NO:72, as well as mature VEGF-E polypeptides and polynucleotides encoding the same.
In another embodiment of the invention, isolated osteoinductive agents include one or more polynucleotides or polypeptides of Transforming Growth Factor-beta genes (“TGF-βs”). TGF-βs are a class of proteins thought to have growth-promoting activities on a range of tissues, including connective tissues. Known members of the TGF-β family include, but are not limited to, TGF-β-1, TGF-β-2, and TGF-β-3.
TGF-βs useful as isolated osteoinductive agents include, but are not limited to, the following TGF-βs:
TGF-β-1 polynucleotides and polypeptides corresponding to SEQ ID NO:73, SEQ ID NO:74, SEQ ID NO:75 and SEQ ID NO:76, as well as mature TGF-β-1 polypeptides and polynucleotides encoding the same.
TGF-β-2 polynucleotides and polypeptides corresponding to SEQ ID NO:77, SEQ ID NO:78, SEQ ID NO:79 and SEQ ID NO:80, as well as mature TGF-β-2 polypeptides and polynucleotides encoding the same.
TGF-β-3 polynucleotides and polypeptides corresponding to SEQ ID NO:81 and SEQ ID NO:82, as well as mature TGF-β-3 polypeptides and polynucleotides encoding the same.
In another embodiment of the invention, isolated osteoinductive agents include polynucleotides and polypeptides promoting bone adhesion, such as Periostin polynucleotides and polypeptides that are thought to function as adhesion molecules in bone formation.
Bone adhesion promoters include, but are not limited to, Periostin polynucleotides and polypeptides corresponding to SEQ ID NO:83 and SEQ ID NO:84, as well as mature Periostin polypeptides and polynucleotides encoding the same.
In another embodiment of the invention, isolated osteoinductive agents include one or more members of any one of Bone Morphogenetic Proteins (BMPs), Connective Tissue Growth Factors (CTGFs), Vascular Endothelial Growth Factors (VEGFs), Osteoprotegerin or any of the other osteoclastogenesis inhibitors, Periostin, and Transforming Growth Factor-betas (TGF-βs).
Methods for producing acetabular cups are well known in the art, and production methods will depend on the desired compositions of the acetabular cup. Exemplary methods of production that may be utilized to generate a porous substrate surface are known in the art and include, but are not limited to, procedures such as machining the substrate material from wrought bar stock or machining components from castings. In an alternative embodiment of the invention, the substrate surface is generated using acetabular cup implant coatings of materials or production methods that generate a porous substrate surface. Acetabular cup coatings include, but are not limited to, ranges of design from a beaded surface with various bead diameters and pore size, to a fiber metal mesh design. Implant coatings are typically applied through a high heat sintering or plasma spray process.
In one embodiment of the invention, the osteoinductive formulations of the invention comprising osteoinductive agents are admixed with sustained release polymers recited supra and applied to the porous surface of the acetabular cup. As noted supra, the duration of sustained release may be manipulated by increasing the resistance to biodegradation of the polymer by, for example, introducing or increasing the percentage of biostable polymers contained within the biodegradable polymer compositions.
In another embodiment of the invention, the acetabular cup comprises, or alternatively consists of, a porous substrate surface comprising osteoinductive formulations. In one embodiment of the invention, the porous substrate surface comprising the osteoinductive formulations is further coated with a biodegradable or bioabsorbable polymer coating. Exemplary biodegradable or bioabsorbable coatings are discussed supra. In another embodiment of the invention, the biodegradable or bioabsorbable polymer coating is provided in the form of a sheath or wrap that is placed over the outer surface of the acetabular cup prior to implantation in the patient.
In another embodiment of the invention, the acetabular cup [ 10 ] comprises, or alternatively consists of, a plurality of microchambers [ 14 ] present in the base material of the acetabular cup, as displayed in FIG. 1 . The plurality of microchambers present in the base material comprise osteoinductive formulations, and are aseptically sealed with biodegradable or current responsive polymers. The osteoinductive formulations comprise one or more osteoinductive agent(s).
Current-responsive polymers include, but are not limited to, those polymers described in U.S. Patent Application Serial No. U.S. 20030007991 as well as those described by Kwon et al. infra, the disclosures of each of which are herein incorporated by reference.
In another embodiment of the invention, the microchambers harboring osteoinductive formulations are sealed with thin films of conductive material patterned in the shape of anodes surrounded by cathodes. Any conductive material that can oxidize and dissolve in solution upon application of an electric potential or current can be used for the fabrication of the anodes and cathodes. Examples of such materials include metals such as copper, gold, silver, and zinc, and some polymers, such as those described for example by I. C. Kwon et al., “Electrically erodible polymer gel for controlled release of drugs”, Nature, 1991, 354, 291-93; and Y. H. Bae et al., “Pulsatile drug release by electric stimulus”, ACS Symposium Series, 1994, 545, 98-110. The anode is defined as the electrode where oxidation occurs. The portion of the anode directly above the microchamber oxidizes and dissolves into solution upon the application of a potential or current between the cathode and anode. This exposes the microchambers to the surrounding fluids and results in the release of the molecules.
Following production of the acetabular cup, a plurality of microchambers may be drilled in the acetabular cup to allow for introduction of the osteoinductive formulations. The number and width of the plurality of microchambers is variable and based on the needs of the patient. For example, the acetabular cup preferably comprises between about 10 to about 100 microchambers in the acetabular cup base. More preferably, the acetabular cup comprises between about 25 to about 75, and still more preferably between about 40 to about 60 microchambers in the acetabular cup base. As one of skill in the art would realize, however, the number and position of microchambers in the acetabular cup base may vary so long as the structural integrity of the acetabular cup is not compromised.
The microchambers provided within the acetabular cup base may be drilled through the full depth of the acetabular cup base. Alternatively, the microchambers may be drilled to a depth of about 1 to about 2 millimeters. Similarly, the width of the microchambers in the acetabular cup may be about 4 to about 6 millimeters in width. On average, the microchamber is about 5 millimeters in width. However, one of skill in the art would realize that the microchamber width may be variable and is based, in part, on the concentration of osteoinductive agent present in the osteoinductive formulation contained within the microchamber. For example, highly concentrated osteoinductive agent(s) will not require a microchamber as wide as osteoinductive formulations comprising weakly concentrated osteoinductive agent(s) in order to achieve delivery of the same concentration of osteoinductive agent(s). Following introduction of the osteoinductive formulations into the microchambers, the microchambers are aseptically sealed with biodegradable or current responsive polymer coatings or plugs that seal the osteoinductive formulations in the microchamber wells, or alternatively with thin films of conductive materials.
In another embodiment of the invention, the acetabular cup is manufactured with electric conductive capacity provided in the acetabular cup compositions. In one embodiment of the invention displayed in FIG. 3 , the acetabular cup [ 20 ] is engineered with at least one electrode secured within the implant coating at the time of manufacture of the acetabular cup. Release of the osteoinductive formulation may be accomplished by either an internal or an external, non-invasive power source applying an electric signal to the electrode contained within the implant coating. In one embodiment of the invention, a plurality of electrode leads [ 22 ] embedded in current responsive polymers seals are conductively attached by a plurality of conductive wires [ 26 ], or comparable conducting materials such as conducting fibers or particles, to a current-providing device [ 28 ]. Current-providing devices are well known in the art, such as for example, current providing devices associated with pace-makers and other implantable biomedical devices
In another embodiment of the invention, current providing devices provide at least one volt of current. One volt of current is considered adequate to melt a thin film coating of gold or other material that seals a microchamber harboring osteoinductive formulations, as discussed supra. However, the invention further contemplates current providing devices that provide greater than one volt of current to a polymer coating or thin film sealant comprising gold or other compounds discussed supra. Current providing devices are further capable of receiving electric signals from interior or exterior sources. Alternatively, electric current is provided to the micro-electrode leads by conducting materials incorporated into the polymers seals. Such conducting materials include, but are not limited to, particles, fibers, patches wires, strands or any other conducting materials that can be incorporated into the polymer plugs and adequately conduct electric current.
In an alternative embodiment of the invention, the acetabular cup is designed to contain microchip drug delivery systems such as those described in U.S. Pat. No. 5,797,898 (which is herein incorporated by reference in its entirety). The chip is designed with several “wells” coated with a current-responsive thin film comprising gold and/or other compound as discussed supra. When current is supplied to the chip, the gold melts, releasing the material. In this embodiment of the invention, the acetabular cup is produced in substantially the same fashion as described for the microchamber-containing acetabular cups. However, instead of providing polymer-sealed microchambers harboring osteoinductive formulations, the acetabular cup relies on microchip drug delivery systems that are incorporated into the acetabular cup. A plurality of reservoirs in the microchip drug delivery system comprise osteoinductive formulations, which are released from the microchip drug delivery systems upon appropriate or pre-programmed stimulus. A plurality of microchips may be implanted into the acetabular cup.
The present invention also relates to vectors containing the osteoinductive polynucleotides of the present invention, host cells, and the production of osteoinductive polypeptides by recombinant techniques. The vector may be, for example, a phage, plasmid, viral, or retroviral vector. Retroviral vectors may be replication competent or replication defective. In the latter case, viral propagation generally will occur only in complementing host cells.
The polynucleotides may be joined to a vector containing a selectable marker for propagation in a host. Generally, a plasmid vector is introduced in a precipitate, such as a calcium phosphate precipitate, or in a complex with a charged lipid. If the vector is a virus, it may be packaged in vitro using an appropriate packaging cell line and then transduced into host cells. Useful vectors include, but are not limited to, plasmids, bacteriophage, insect and animal cell vectors, retroviruses, cosmids, and other single and double-stranded viruses.
The polynucleotide insert should be operatively linked to an appropriate promoter, such as the phage lambda PL promoter, the E. coli lac, trp, phoA and tac promoters, the SV40 early and late promoters and promoters of retroviral LTRs, to name a few. Other suitable promoters will be known to the skilled artisan. The expression constructs will further contain sites for transcription initiation, termination, origin of replication sequence, and, in the transcribed region, a ribosome binding site for translation. The coding portion of the transcripts expressed by the constructs will preferably include a translation initiating codon at the beginning and a termination codon (UAA, UGA or UAG) appropriately positioned at the end of the polypeptide to be translated.
The expression construct may further contain sequences such as enhancer sequences, efficient RNA processing signals such as splicing and polyadenylation signals, sequences that enhance translation efficiency, and sequences that enhance protein secretion.
Expression systems and methods of producing osteoinductive agents, such as recombinant proteins or protein fragments, are well known in the art. For example, methods of producing recombinant proteins or fragments thereof using bacterial, insect or mammalian expression systems are well known in the art. (See, e.g., Molecular Biotechnology: Principles and Applications of Recombinant DNA, B. R. Glick and J. Pasternak, and M. M. Bendig, Genetic Engineering, 7, pp. 91-127 (1988), for a general discussion of recombinant protein production).
The expression vectors will preferably include at least one selectable marker. Such markers include dihydrofolate reductase, G418 or neomycin resistance for eukaryotic cell culture and tetracycline, kanamycin or ampicillin resistance genes for culturing in E. coli and other bacteria. Representative examples of appropriate host cells for expression include, but are not limited to, bacterial cells, such as E. coli, Streptomyces and Salmonella typhimurium cells; fungal cells, such as Pichia and other yeast cells; insect cells such as Drosophila S2 and Spodoptera Sf9 and Sf21 cells; animal cells such as CHO, COS, 293, and Bowes melanoma cells; and plant cells. Appropriate culture mediums and conditions for the above-described host cells are known in the art.
Examples of vectors for use in prokaryotes include pQE30Xa and other pQE vectors available as components in pQE expression systems available from QIAGEN, Inc. (Valencia, Calif.); pBluescript vectors, Phagescript vectors, pNH8A, pNH16a, pNH18A, pNH46A, available from Stratagene Cloning Systems, Inc. (La Jolla, Calif.); and Champion™, T7, and pBAD vectors available from Invitrogen (Carlsbad, Calif.). Other suitable vectors will be readily apparent to the skilled artisan.
Introduction of the construct into the host cell can be effected by calcium phosphate transfection, DEAE-dextran mediated transfection, cationic lipid-mediated transfection, electroporation, transduction, infection, or other methods. Such methods are described in many standard laboratory manuals, such as Davis et al., Basic Methods In Molecular Biology (1986).
A polypeptide of this invention can be recovered and purified from recombinant cell cultures by well-known methods including ammonium sulfate or ethanol precipitation, acid extraction, anion or cation exchange chromatography, phosphocellulose chromatography, hydrophobic interaction chromatography, affinity chromatography, hydroxylapatite chromatography and lectin chromatography. Most preferably, high performance liquid chromatography (“HPLC”) is employed for purification.
In another embodiment of the invention, osteoinductive agents can be produced using bacterial lysates in cell-free expression systems that are well known in the art. Commercially available examples of cell-free protein synthesis systems include the EasyXpress System from Qiagen, Inc. (Valencia, Calif.).
Polypeptides of the present invention can also be recovered from the following: products of chemical synthetic procedures; and products produced by recombinant techniques from a prokaryotic or eukaryotic host, including, for example, bacterial, yeast, higher plant, insect, and mammalian cells.
Depending upon the host employed in a recombinant production procedure, the polypeptides of the present invention may be glycosylated or may be non-glycosylated. In addition, polypeptides of the invention may also include an initial modified methionine residue, in some cases as a result of host-mediated processes. Thus, it is well known in the art that the N-terminal methionine encoded by the translation initiation codon generally is removed with high efficiency from any protein after translation in all eukaryotic cells. While the N-terminal methionine on most proteins also is efficiently removed in most prokaryotes, for some proteins, this prokaryotic removal process is inefficient, depending on the nature of the amino acid to which the N-terminal methionine is covalently linked.
The osteoinductive agents of the invention may also be isolated from natural sources of polypeptide. Osteoinductive agents may be purified from tissue sources, preferably mammalian tissue sources, using conventional physical, immunological and chemical separation techniques known to those of skill in the art. Appropriate tissue sources for the desired osteoinductive agents are known or are available to those of skill in the art.
The acetabular cups of the invention are useful in hip replacement surgeries, as components of total hip replacements. The acetabular cups of the invention are particularly useful in providing formulations that enable ingrowth of the patient's endogenous pelvic bone into the acetabular cup, thereby enhancing the structure and strength of the implant.
Another advantage provided by the acetabular cup of the invention is that the acetabular cup provides a reservoir of osteoinductive formulations that continue to promote bone ingrowth into the acetabular cup implant over extended periods of time, thereby helping to strengthen and secure the acetabular cup implant over extended periods of time and use.
The acetabular cup of the invention also mitigates the damage caused by wear debris and osteolysis by releasing osteoinductive formulations over extended periods of time, thereby continuously promoting osteoinduction, treatment of osteolytic lesions, and securing the acetabular cup to the pelvic bone. Polyethylene wear debris in total joint implantations can lead to osteolysis at the site of implantation. The development of osteolysis over time can lead to implant loosening and require implant revision. Traditional treatment of osteolytic lesion(s) requires surgery to remove the primary components, followed by treatment of the lesion(s) with allograft materials and re-implant revision components. The acetabular cup of the invention addresses these concerns through the osteoinductive capacity of the acetabular cup.
Surgeons skilled in the art of hip replacement are best able to determine whether a given patient is in need of enhanced ingrowth of pelvic bone into the acetabular cup of the invention. As a result, the acetabular cup of the invention is available with variable concentrations of osteoinductive compositions comprising osteoinductive agent(s).
The acetabular cup of the invention further provides for the sustained release of osteoinductive agent(s) over extended periods of time. In one embodiment of the invention, the osteoinductive agent(s) is provided for a period of time of about 10 months to about 48 months. The sustained release of the osteoinductive formulations over a period of time can be achieved in a number of ways. For example, by providing biodegradable polymer seals having differing rates of biodegradation, the acetabular cup provides osetoinductive formulations which release osteoinductive agent(s) in bioavailable form at rates directly proportional to the rates of polymer degradation in vivo. Similarly, where the osteoinductive formulations are liberated from the microchambers by application of electric potential or current, the potential or current providing device can be programmed or engineered to provide current to different microchambers at differing times throughout the life of the acetabular cup implant, thereby liberating osteoinductive agent(s) in bioavailable form at pre-programmed times. Likewise, where the osteoinductive formulations are liberated from microchip drug delivery systems, the microchip device can be programmed or engineered to release osteoinductive formulations at differing times throughout the life of the acetabular cup, thereby liberating osteoinductive agent(s) in bioavailable form at pre-programmed times.
In an additional aspect of the invention, the acetabular cup compositions of the invention are packaged in kits under sterile conditions based on the desired duration of release of osteoinductive formulation. More particularly, it is believed that an implant surgeon skilled in the art of acetabular cup implantation and hip replacement is best able to ascertain and judge the degree and duration of osteoinductive activity desired in any given patient. Accordingly, the acetabular cups of the invention provide osteoinductive formulations in immediate release formulations as well as sustained release formulations. The sustained release formulations optionally provide osteoinductive formulations for short periods of time or extended periods of time. By extended periods of time is meant a sustained release formulation that provides bioavailable osteoinductive formulations not earlier than about 10-12 months following implantation, and preferably provides bioavailable osteoinductive formulations up to about 4 years in time.
Similarly, the kits of the invention provide osteoinductive formulations of differing concentration based on the desired degree of osteoinductive activity. Typical osteoinductive formulations comprise osteoinductive agent at concentrations of from about 0.1 mg/ml to 100 mg/ml, preferably 1-10 mg/ml, at a pH of about 3 to 8.
The kits of the invention further optionally comprises instructions for the preparation and administration of the osteoinductive formulations and the orthopaedic device.
The invention may be practiced in ways other than those particularly described in the foregoing description and examples. Numerous modifications and variations of the invention are possible in light of the above teachings and, therefore, are within the scope of the appended claims.
The entire disclosure of each document cited (including patents, patent applications, journal articles, abstracts, manuals, books, or other disclosures) in the Background of the Invention, Detailed Description, and Examples is herein incorporated by reference in their entireties.
EXAMPLES
I. Implantation of an Acetabular Cup with a Porous Substrate
A patient in need of hip replacement receives hip replacement surgery wherein an acetabular cup of the invention is implanted. The acetabular cup comprises a porous coating into which a sustained release osteoinductive formulation is impregnated. The osteoinductive formulation further comprises mature BMP-2 polypeptides and mature osteoprotegerin polypeptides in concentrations of about 1 mg/ml to 10 mg/ml. The osteoinductive formulation further comprises one or more antibiotics. The sustained release formulation comprises a biodegradable polymer that releases osteoinductive formulation at a rate consistent with biodegradation of the polymer.
The acetabular cup is monitored by X-ray examination over the following five years for signs of osteolysis or weakening of the acetabular cup implant. Evidence of endogenous bone in-growth without evidence of osteolysis indicates that the osteoinductive formulation stimulates bone in-growth into the acetabular cup, thereby securing the acetabular cup and increasing the success of the implant.
II. Implantation of an Acetabular Cup with Microchambers
A patient in need of hip replacement receives hip replacement surgery wherein an acetabular cup of the invention is implanted. The acetabular cup comprises a plurality of microchambers into which sustained release osteoinductive formulations are administered. The osteoinductive formulation further comprises mature BMP-2 polypeptides and mature osteoprotegerin polypeptides in concentrations of about 1 mg/ml to 10 mg/ml. The osteoinductive formulation further comprises one or more antibiotics. The microchambers are sealed with a biodegradable polymer that releases osteoinductive formulation from the plurality of microchambers at a rate consistent with biodegradation of the polymer.
The acetabular cup is monitored by X-ray examination over the following five years for signs of osteolysis or weakening of the acetabular cup implant. Evidence of endogenous bone in-growth without evidence of osteolysis indicates that the osteoinductive formulation stimulates bone in-growth into the acetabular cup, thereby securing the acetabular cup and increasing the success of the implant.