Title:  Hydroxyapatite based drug delivery implant for cancer treatment

United States Patent:  6,767,550

Issued:  July 27, 2004

Inventors:  Genin; Fran.cedilla.ois Y. (Berkeley, CA); Luo; Ping (Berkeley, CA); Dash; Alekha K. (Omaha, NE)

Assignee:  Berkeley Advanced Biomaterials, Inc. (Berkeley, CA)

Appl. No.:  608488

Filed:  June 30, 2000

Abstract

A hydroxyapatite based bioresorbable material is incorporated with anti-cancer agents to form an implant used for treatment against cancer. Sustained release of the anti-cancer agents may be achieved after implantation at the targeted sites. The dosage of the anti-cancer agent, the microstructure, morphology, and composition of the bioresorbable material allow control of the release profile. The invented implant may be used for drug delivery, chemotherapy, or gene therapy.

SUMMARY OF THE INVENTION

We have invented a novel method to deliver anti-cancer agents in desired concentrations, wherein the dosage form, which anti-cancer agents such as doxorubicin are incorporated into a biocompatible matrix material, is an implant. The therapeutic method includes administering the drug topically, systemically, or locally as an implant or device. The drug is preferably used for bone or cartilage cancer treatment. The implant can be directly placed within or around the bone or cartilage adjacent to the tumor. This mode of treatment has the following advantages:

1. rapid reduction in the mass and size of primary tumors; this could increase the possibility of organ-salvage surgery and thereby accelerate patient rehabilitation after surgery),

2. decreased likelihood of metastasis after initiation of treatment because of the rapid reduction in the number of tumor cells,

3. virtual elimination of the systemic side effects because of the smaller dose used and its confinement to a local site.

Human bone is known to contain on average about 70% minerals. The minerals are in majority composed of hydroxyapatite, carbonate apatite, and calcium phosphates. Fluoroapatite has also been reported to occur in bones such as teeth. The biocompatible materials described in this invention include any bioresorbable materials such as collagen, calcium sulfate, bioactive glass, bioresorbable polymer, single-phase hydroxyapatite or multiphase calcium phosphates (crystalline or amorphous). The choice of the biocompatible matrix is determined to control the resorption rate of the implant and the release rate of the anti-cancer agent. Clinical studies proved that bioresorbable materials promote bone growth. The porosity of the implant improves osteo-conduction and osteo-induction. The resorption rate can be tailored by controlling the degree of crystallinity, the microstructure, and the morphology of the implant. The implant can be fully resorbed after a period of time that can range from 2 weeks to 24 months.

Many anti-cancer agents can be incorporated into biocompatible materials to form the implant. Among the anti-cancer agents available today, the most effective for treating bone cancer is doxorubincin. The implant can be used for targeted chemotherapy. The implant can be surgically placed at or around the tumor site or within the bone directly adjacent to the tumor. After implantation, the anti-cancer agents are released continuously or periodically from the implant at a desired rate. Periodical release can be achieved with for example a multi-layered tablet of pure hydroxyapatite and hydroxyapatite loaded with anti-cancer agents. The anti-cancer molecules then approach the tumor cells preferentially as a result of their proximity.

Several therapeutic delivery systems were developed and patented. Unger et al. describe in U.S. Pat. No. 5,542,935 a system comprising of gaseous precursor-filled microspheres, in which doxorubicin are encapsulated.

In U.S. Pat. No. 5,656,108, Nies et al. describe a process to prepare porous bone replacement materials composed mainly of acrylate/methacrylate. Hydroxyapatite particles are used as an additive and are not in excess of about 30% by weight. Active compounds such as doxorubicin are added to the constituents of bone cements and hardened to form an implant. In the present invention, the biocompatible material such as hydroxyapatite is greater than 70% by weight, which is the main phase of the drug delivery implant.

In U.S. Pat. No. 5,797,873, Franz et al. describes a process to prepare bone cements comprising of active compounds including doxorubicin. The bone cement is composed of a solid component and a liquid component. The solid component is about 50% to 75% by weight. The active component is dissolved into an organic solvent. Hydroxyapatite is used as an additive.

In U.S. Pat. No. 5,968,253, Poser et al. describe a process to prepare calcium phosphate cements comprising anti-microbial agents. A flowable compound containing calcium phosphates and a liquid lubricant loaded with anti-microbial agent becomes an apatitic product such as hydroxyapatite after injection into the body. The anti-microbial agents are from the group consisting of gentamycin and vancomycin.

Other drug delivery systems have been invented to treat bone infections. U.S. Pat. No. 5,514,137, by Coutts describes an orthopedic device made of a cement composed of hydroxyapatite, ortho-phosphoric acid, calcium carbonate, and calcium hydroxide. The cement material contains an active agent selected from the group consisting of antibiotics, bone growth promoters, vasoactive agents, and other drugs to prevent or mitigate infection. U.S. Pat. Nos. 5,939,380, and 5,110,595, by Wang describes a process of producing implants containing bioactive macromolecules for sustained delivery. A lipid powder is mixed with bioactive polypeptides and compressed into disc or rod-shaped implants. This polymer based drug delivery implant is mixed with insulin, which is a polypeptide hormone, with a concentration of up to 40% by weight. This type of device can hold a sufficient amount of active proteins to sustain the desired therapeutic effect for many weeks.

Further, in U.S. Pat. No. 5,780,044, Yewey, et al, described biocompatible liquid delivery compositions, which provide sustained release of active agents. The liquid delivery compound consists a biocompatible polymer or prepolymer in combination with an active agent such as doxorubicin. The liquid delivery system may be introduced into the body and it solidifies or cures in situ to form a controlled release implant or a film dressing. The liquid delivery compound may also be employed ex situ to produce a controlled release implant.

Various types of drug delivery systems formulated with anti-cancer agents include drug-antibody complexes, albumin microspheres, ferromagnetic or ethyl cellulose micro-capsules, biodegradable micro-capsules, and liposomes [Kato, T., in Controlled Drug Delivery, Vol. 11, Clinical Applications, ed. Bruck, S. D., CRC Press, Boca Raton, Fla., (1983) pp. 189-240 and Davigonon, J. P. and Craddock, J. C., in Fundamentals of Cancer Chemotherapy, eds. Hellmann, K. and Carter, S. K., McGraw-Hill, New York, N.Y., (1987) pp. 212-217]. Most of these dosage forms have been formulated for parenteral administration. Although these drug delivery systems have found a variety of uses in targeting certain forms of cancer, their suitability to treat bone cancer has not yet been demonstrated.

Polydimethylsiloxane (PDMS) is an inorganic synthetic and biocompatible polymer that is used popularly as a drug delivery matrix. The medical-grade silicone is prepared from PDMS. It has been successfully used in sustained- and controlled-release drug delivery systems. The release rate of lipophilic drugs such as progesterone and testosterone from silicone polymers is several orders of magnitude higher than from organic polymers. However, the release rate of hydrophilic drugs incorporated into silicone implants is very low. The addition of some hydrophilic compounds, such as glycerol, to the polymer matrix greatly enhances the release rate of several hydrophilic drugs. Unfortunately, the shelf-life of such implantable drug delivery system is short due to the instability of the polymer matrix with the addition of glycerol [Dash, A. K. and Suryanarayanan, R. (1992) An implantable dosage form for the treatment of bone infections. Pharm. Res. 9: 993-1002].

Implantable biodegradable polymer (Poly-lactic-glycolic acid) micro-capsules containing gentamycin and ciprofloxacin have been prepared and evaluated in the treatment of osteomyelitis [Sampath, S. S., Garvin, K. and Robinson, D. H. (1992) Preparation and characterization of biodegradable poly(lactic/glycolide) (50:50)-gentamycin delivery systems. Int. J. Pharm. 78:174 and Ramehandani, M. and Robinson, D. H. (1998) In vitro and in vivo release of ciprofloxacin from PLGA 50:50 implants, J. Control. Rel. 54:167-175]. The advantage of this approach is that the dosage form needs not be removed from the body at any time. Resorption of the implant was observed to occur in 6 to 8 weeks, which is longer than expected. Sub-therapeutic concentrations of antibiotics in the bone for an extended time period could also lead to the development of resistant organisms. Moreover, prolonged exposure to the antibiotics could lead to hypersensitivity reactions [Schurman, D. J., Trindade, C., Hirshman, H. P., Moser, K., Kajiyama, G. and Stevens, P. Antibiotic-acrylic bone cement composites: studies of gentamycin and Palacos. J. Bone. Joint Surg. 60A, (1978), pp. 978-984]. More importantly toxic organic solvent like methylene chloride is generally used for their complex fabrication procedure.

Hydroxyapatite, tri-calcium phosphate, and amino acid antibiotic composite ceramics are some of the most biocompatible and bioresorbable synthetic hard tissue implant materials. When they are combined with amino acids in water, the resultant formulation provides a composite which sets with similar consistency to cement that is free of both local and systemic toxicity. They directly bond to bone via natural mechanisms, thus allowing for utilization to stabilize traumatized bone fractures. When loaded with antibiotics, such systems can also release the drug at therapeutic concentrations directly to the infected area [Morris, L. and Bajpai, P. K., Development of a resorbable tri-calcium phosphate amine antibiotic composite in biomedical materials and devices, Eds. Hanker, J. S. and Giammara, Pittsburgh, Pa.: Materials Research Society, (1989) pp. 293-300]. Hydroxyapatite and tri-calcium phosphates containing cysteine or lysine composites loaded with erythromycin or penicillin have been developed for the treatment of bone infections. The results revealed that a constant release of antibiotics was obtained over a period of 3 weeks at the site of infection. This study suggests that antibiotics released from tri-calcium phosphate amino acid composites can be effectively utilized in the treatment of bone infections.

The implant of this invention is capable of releasing the anti-cancer agent over the entire period of resorption. To achieve a fast resorption rate, calcium sulfate and amorphous or nanocrystalline hydroxyapatite drug delivery carriers are excellent candidates. On the other hand, bioactive glass is more suitable to achieve slow resorption rates. A mixture or a multi-layered structure of pure and drug-loaded biomaterials can form an implant for which the resorption rate is designed.

The release rate and release profile can be tailored by the morphologies of the biocompatible implant in this invention. The results of the in vitro release tests in examples 1 and 2 for hydroxyapatite granules and discs respectively showed that the granular implants release doxorubicin much faster than the disc implants. More complex release profiles can be obtained from mixtures of implants with different microstructures and geometry.

The implants may be heterogeneously or homogeneously mixed with the bio-molecules depending on their concentration, the composition of the biocompatible materials, and the implant processing pressure.

The implants may be dense or porous. Porous implants provide pathways for fast diffusion and lead to quicker delivery than dense implants. The pore sizes of porous implants can be tailored from 1 micron to 3 mm depending on the desired release profiles.

Anti-cancer agent incorporation into an implant is achieved by dissolving the agent in water or solvents and mixing it with the biocompatible materials such as hydroxyapatite powder to form a slurry. The slurry can then be dried into granular implant with desired shapes using a large variety of commercially available equipment, such as a spray dryer, a vacuum dryer, or a fluidized bed. The drying temperature ranges from room temperature to 150^oC. to avoid decomposition of the anti-cancer agent. In U.S. Pat. No. 5,858,318, Luo, P. described a process producing hydroxyapatite microspheres, hollow spheres, and doughnut-shaped particles by controlling the spray drying parameters. A foaming agent e.g. ammonium hydroxide was co-sprayed to form interconnected micropores.

In addition, the slurry can be dried into a paste and then formed into desired shapes by casting methods. The granular implant in this invention is formed into a cylindrical shape. The diameter of the cylinder depends on the size of hole on the mold. Furthermore, the paste can be injected with a foaming agent into a mold with desired geometry such as square, rectangle, disc, cylinder, and sphere. The concentration of the foaming agent and the process temperatures control the pore size of the block implant.

A simple method can be used to form block implants using a press and dies with different diameters. Biocompatible binding agents can be used to form the disc implant if low pressures are applied.

The block implant can be incorporated homogeneously or heterogeneously with the anti-cancer agent. Homogenous implants can be obtained by loading a low concentration of the anti-cancer agent. Forming into desired shapes at various pressures and mixing with biodegradable polymers such as collagen, gelatin, and polymer in various compositions can also result in a homogenous implant.

A method to use the implant material of this invention is also provided. To demonstrate the method, the hydroxyapatite drug delivery implant is implanted surgically within the bone or the cartilage either into the tumor or around it. The implant can be placed in the void after a tumor is removed to continue treatment therapeutically. Since hydroxyapatite is osteoinductive and osteoconductive, the void can be replaced by new bone after the completion of the release and the resorption of the implant.

The term "bioresorbable materials" refers to a group of materials that have been shown to clinically resorb in the human body. The bioresorbable materials in this invention include calcium phosphates, hydroxyapatite, apatites, calcium sulfates, bioresorbable polymers, collagen, gelatin, and bioactive glass. Calcium phosphates include alpha-tri-calcium phosphate and beta-tri-calcium phosphate.

The term "anti-cancer agents" includes all bioactive agents that can kill or inhibit the growth of cancer cells. This includes proteins, peptides, DNA molecules, and hormones, which can be incorporated into the implant to increase the delivery efficacy and treat against cancer. The concentrations of the incorporation range from 0.0001% to 30% by weight. The anti-cancer agents diffuse out of the body of the implant into the targeted site.

Claim 1 of 9 Claims

What is claimed is:

1. A two layered, sustained release, biocompatible implant comprising a first layer consisting of pure hydroxyapatite and a second layer comprising hydroxyapatite, a bioresorbable material, and doxorubicin homogeneously distributed in amounts from 0.0001 to 30% by weight.

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