WO1993015767A1

WO1993015767A1 - Implant therapy for bone growth stimulation

Info

Publication number: WO1993015767A1
Application number: PCT/US1993/000946
Authority: WO
Inventors: Leah E. Appel; Gaylen M. Zentner; Gideon A. Rodan
Original assignee: Merck & Co., Inc.
Priority date: 1992-02-05
Filing date: 1993-02-04
Publication date: 1993-08-19
Also published as: AU3607293A

Abstract

Therapeutic stimulation of bone formation is accomplished through the controlled release of the prostaglandins E1, E2 or F2α, or the steroid, β-estradiol to the site where bone growth stimulation is desired. A rigid, solid, controlled release dosage form, consisting of a non-residue producing, bioerodible polymer, selected from a poly(ortho ester) or a polyacetal and a prostaglandin, or β-estradiol is implanted at the site of desired bone growth stimulation. The figure shows E2 release at .81 (Group A), .035 (Group B) and .003 (Group C) weight %.

Description

TITLE OF INVENTION

IMPLANT THERAPY FOR BONE GROWTH STIMULATION

FIELD OF THE INVENTION

The present invention comprises both a useful and novel method of stimulating bone formation. The method utilizes a drug-delivery device which releases prostaglandin E₂, hereinafter PGE₂, to a specific section of bone, in a therapeu- tically effective manner, whereby bone formation is stimulated. Particularly, the invention pertains to the implantation of a bioerodible polymer drug delivery device containing PGE₂, which is implanted at a site in or near the bone of a mammal, and which delivers a therapeutically effective amount of PGE_? to the bone over an extended period of time, resulting in bone formation and bone development in an unexpected reduced time period.

SUBSTITUTE SHEET The function of this device is dependent upon proper placement in or near the bone in need of therapy. The device is positioned as close as possible to the site of therapy, thereby maximizing target site drug delivery while minimizing the systemic uptake of drug. That is, by placing the device in close proximity to the target treatment area, higher concentration of the released PGE₂ can be utilized in the bone formation process. This allows for delivery of higher therapeutic levels of PGE₂ to the bone and less distribution to other organs and tissue of the body.

Placement of the device at the site of a bone fracture has resulted in unexpectedly rapid healing of the bone and development of dense bone matter around the area of the break.

BACKGROUND OF THE INVENTION

The need for a procedure that promotes the development of dense bone in areas of fracture or weakness, and reduces the time required for the repair of broken bones is well established. Several studies attempting to induce bone development have been reported.

Studies using hormones such as parahyroid hormone (PTH), 1,25-dihydroxyvitamin D₃ and GE_2> as well as cytokines such as lymphotoxin, interleukin-1, tumor necrosis factor, epidermal growth factore and transforming growth factor have demonstrated some ability to affect bone resorption both in vivo and i vitro. It is thought that these agents exhibit an effect on intermediary cells which

SUBSTITUTESHEET are involved in resorption. Hayward, M. and Fiedler-Nagy, Ch. , Agents and Actions, 22, 251-254 (1987). PGE₂ has also been implicated in bone loss. See Hayward, M. A. and Caggiano, T. J. , Annual Reports in Medicinal Chemistry, 22, Sect. IV, Chapter 17, 169-178 (1987).

U.S. patent 4,621,100 discloses a method for treatment or prevention of non-growth related osteoporosis in an animal, based upon oral administration of PGE₂ and intravenous administration of prostaglandin E, . Bone growth effects were observed after ninety days of oral PGE₂ therapy. These results included an increase in bone turnover, including increased activation, resorption and formation rates. Side effects of oral dosing of GE₂ such as loose stools, diarrhea, vomiting, injected sclerae, and increased serum alkaline phosphatase were observed during the dosing period. Toxicity, due to systemic distribution of

PGE₂, has reduced the pharmaceutical utility of this compound. Delivery of PGE₂ in a non-specific manner requires elevated concentrations of the drug and as noted in U.S. patent 4,621,100 results in unwanted side effects.

British patent 1,494,463 discloses that therapeutic levels of PGE₂ results in increased blood pressure, stimulated smooth muscle reactions, inhibited gastric secretion, controlled spasm and facilitated breathing in asthmatic conditions, decongested nasal passages, decreased blood platelet adhesion and has affected the reproductive organs of

SUBSTITUTE SRΞE? mammals as a labor inducer, abortifacien , cervical dilator, regulator of the estrus and regulator of the menstrual cycle.

Delivery of GE₂ in a polymer based controlled dosage form has been suggested in U.S. patents 4,093,709 and 4,639,366. However, a method for delivering E₂ directly to the site of the bone or the use of a controlled release device to deliver PGE₂ to the site of a broken bone has not been reported.

WO-90-15586 teaches a controlled release drug delivery device comprising a bioerodible polymer admixed with gentamicin. The device was implanted in bone that had been inoculated with Staphylococcus aureus to induce osteomyelitis in rats. A polymer composed of poly(propylene fu arate) prepolymer crosslinked with methylmethacrylate was used as a matrix for the implantation and controlled release of the antibiotic. The medicament, supplied as a paste composed of the polymer and the antiboitic was able to reduce the degree of infection. The polymer used by this system decomposed to non-toxic residues.

WO-90-15586 further teaches the use of this paste for the delivery of Insulin Growth Factor 1, hereinafter IGF, as a means of enhancing bone formation. A twelve week treatment period is recommended.

However, as shown in Example 1 of the present invention, a study which compared controlled infusion of IGF, and PGE_2> demonstrated that controlled delivery of IGF, did not promote bone growth as taught by this reference. Further, as

SUBSTITUTESHEET Example 2 demonstrates, enhanced bone growth stimulation using site specific, controlled dosing of PGE₂, can be accomplished in much less time than would have been expected based on the reports using IGF, treatment.

SUMMARY OF THE INVENTION

This invention is concerned with a novel method of promoting bone growth which is useful in the treatment of bone fractures, osteoporosis, osteopenia or the like, which comprises the slow controlled release of therapuetic levels of PGE₂ at the sige where bone growth stimulation is required. A novel device useful for the slow controlled release of PGE₂ at the desired site, which forms another embodiment of this invention, is an implantable biodegradable dosage form, consisting essentially of a bioerodible polymer selected from a poly(ortho ester) or a polyacetal and the bone-growth promoting agent, PGE₂. The polymer used in this device completely degrades to compounds which are water soluble and are excreted from the body in such a manner that a decomposition residue does not remain in the implant area.

By placing the controled release dosage from containing PGE„ at the site where bone growth stimulation is required, side effects normally seen during treatment by traditional routes of administration with this compound were not observed.

f-> > fffT?*"' t I¹' ~ 1 1^"«""1 DETAILED DESCRIPTION OF THE INVENTION

The novel method of this invention comprises the stimulation of bone growth by the administration of PGE₂, in a controlled release manner at a sige at which bone growth stimulation is desired.

The stimulation of bone growth is useful in the treatment of bone fractures, osteoporosis, osteopenia or the like.

By stimulation of bone growth is meant enhanced recruitment of bone forming cells, their differentiation and functions as matrix forming cells about the area of bone fracture.

By administration of PGE₂ is meant the release of free PGE₂ from any delivery device, media or matrix intended to function as a transportation or storage media for the PGE₂- The term "free PGE₂" refers to the PGE₂ which is released from the dosage form and available for therapeutic use. "Free PGE₂" is the PGE₂ medicament which is administered to the site where bone growth stimulation is desired, in a controlled release manner.

By "controlled release manner" is mean delivery of free PGE₂ to the site where bone stimulation is required at a predetermined, therapeutic rate. The duration of the delivery of PGE₂ to affect therapeutic stimulation of bone growth, is maintained for a period of time that is dependent upon the condition being treated.

By "site at which bone growth stimulation is desired" is meant, both the area adjacent to a section of bone of group of bones in need of

SUBSTITUTESHEET treatment or a region inside the bone including the site of a fracture or opening which occurs naturally or is intentionally made in the bone or group of bones where treatment can be administered.

Stimulation at the site where bone growth is desired also may be accomplished by infusing a solution containing PGE₂ into the treatment area. However, this procedure is inconvenient and of little practical value in the treatment of bone disease or fracture. More conveniently, a controlled release dosage from, designed for controlled delivery of PGE₂, can be implanted at the desired location of, either adjacent to the site or within the bone. The present method is particularly versatile and can be applied to the stimulation of bone growth at the site of a broken bone or a region of bone affected by osteoporosis or osteopenia or the like. The novel method of treatment of this invention is not meant to be limited to these bone conditions, since those skilled in the art would recognize other bone conditions in need of this therapy.

By broken bone is meant all types of broken bones i.e. green stick fracture, compound fracture, lateral fracture, pathologic fractures resulting from invasive tumors, compression fractures, fractures that require surgical procedures for realignment of bones, etc.

By osteoporosis in meant a reduction in bone matter associated with an increased risk of bone fracture. This term includes what is sometimes called osteopenia.

SUBSTITUTE SHEET Stimulation of bone growth, utilizing this procedure, requires the daily delivery of about 0.01 μg to about 100 μg of 0GE₂ to the site at which bone growth stimulation is desired. By "about 0.01 μg to about 100 μg of PGE₂" is meant that during the course of any 24 hour period, the procedure requires delivery of an amount of PGE₂ that is within this range and that deviations at either extreme of the range of up to 507_ can be tolerated once the treatment regiment is established.

This procedure provides for delivery of PGE , in an uninterrupted manner, for from about 1 to about 28 days. By "uninterrupted manner" is meant, that the device will deliver PGE₂ to the area in need of therapy, for a sustained period of time, at an average daily dose level of PGE₂ of about 0.01 μg/day to about lOOμg/day. The actual level of PGE₂ delivered is dependent upon the therapeutic level required for the specific treatment regimen.

Under certain circumstances, release of PGE₂ may not occur immediately upon the initiation of treatment. However, within twelve to thirty six hours, delivery of PGE₂ to the area in need of therapy will commence.

One embodiment of the novel device of this invention comprises a biodegradable dosage form consisting essentially of a bioerodible polymer and PGE₂. The dosage form is designed to release free PGE₂ to the area in need of therapy at a desired rate. The novel device of this invention, is designed for easy implantation either adjacent to the bone or within the bone in need of therapy.

SUBSTITUTE SHEET The procedure involves the surgical implantation of a controlled release dosage form which dispenses PGE₂ at the site of bone fracture. As bioerosion of the polymer occurs, PGE₂ is released directly ot the site where new bone growth is required.

By surgical implantation is meant utilizing aseptic technique; cutting open the skin, muscle or other tissue to expose the bone in the area where stimulation of bone growth is required; placing the dosage form either into the boen or adjacent to the bone, that is, as close to the bone as possible; and then closing the disturbed tissue, muscle and skin using standard medical techniques. Techniques such as arthroscopy, and any other invasive methods which would allow the placement of the dosage form within or near a bone in need of growth stimulation therapy would also be included within this definition. By "bioerosion" or "bioerodible" or "erosion" or "erodes" is meant the process, including hydrolysis, dissolution, abrasion, and corrosion, by which the dosage form is reduced in size due to the chemical or physical action of the aqueous fluids, bone and tissue present in the area of surgical implantation.

The bioerodible polymer useful in the novel device of this invention are those that completely degrade to compounds which are water soluble and are easily excreted from the body of a subject in need of treatment, in such a manner that no decomposition residue remains at the implant area following release of all of the PGE₂.

SUBSTITUTESHEET By "subject" is meant humans, other mammals, amphibians and any other animal which is partially composed of bone.

The novel device includes sufficient PGE₂ to release O.Olμg/day to 100 μg/day to PGE₂ over a period of time required for ininterrupted therapy. The bioerodible polymer is a poly(ortho ester) such as or a polyacetal such as ....

A variety of polymers exist that have the characteristics necessary to deliver PGE₂ to the site of a bone fracture. That is, the polymer must be compatible with the biological environment where therapy is to be delivered. By compatibility is meant, that the polymer must be non-toxic and non-mutagenic. In addition, since the device may be implanted at the site of a break in a bone, it must not creat more than a minimal inflammatory reaction.

The polymers useful in this system must also be pharmaceutically acceptable that is, in admixtures with the PGE₂, a uniform product must result. Since the polymer is the primary component, by weight, in the dosage form, it must support homogeneous admixture with PGE₂. Admixtures can be accomplished by a number of means that are known by those skilled in the pharmaceutical arts such as simple compounding of ground polymer and PGE~ followed by compression into forms suitable for implantation or by granulating the polymer and PGE₂ with a suitable solvent. After mixing, the solvent is evaporated leaving behind a homogeneous mixture of polymer and PGE₂. In the later procedure, PGE₂ need not be soluble in the solvent.

SUBSTITUTE SHEET A further procedure involves mixing the PGE₂ with the monomers prior to the polymerization step. During the polymerization step the mixture is stirred so that the PGE₂ is homogeneously mixed with the forming polymer.

The final dosage forms can be prepared by compressing the dried mixture of polymer and PGE₂ into the desired form. Other techniques, known to those skilled in the art can also be utilized. The polymer must reproducibly bioerode, in the environment of use, and result in products that are cleared from tissue surrounding the site of bone fracture and ultimately excreted from the body. The release of PGE₂ from a polymer matrix is dependent on the erosion rate of the polymer with which it is admixed. Therefore, the polymer/PGE₂ formulation must result in a dosage form that erodes, in the environment of use, at a predictable rate, resulting in the complete release of PGE₂ to the site of bone therapy. Side reactions that would retard release of PGE₂ are avoided by proper choice of a polymer.

Since the polymer is implanted, sterility of the device must be maintained. This is most easily accomplished with sterile components and utilizing aseptic techniques during a mixing and manufacture of the device. Other methods to assure a sterile product can be employed provided they do not degrade the polymer or PGE₂.

There are many polymers which meet the criteria for this type of implant. The use of any of these that deliver PGE₂, at the desired rate, to the site in need of bone therapy, are considered within the scope of this invention.

SUBSTITUTESHEET Poly(ortho esters) have been utilized in pharmaceutically acceptable controlled release devices in the past mainly becuase they erode in a controlled manner via hydrolysis. One example of a polymer that meets the criteria of this novel procedure has the formula.

The synthesis of this polymer is described in U.S. patent 4,304,767. The polymerization proceeds through a condensation reaction between a ketene acetal and an alcohol. There are no reaction by-products that need to be removed in order to achieve a high molecular weight polymer. The polymer utilized in one embodiment and in example 2 has a molecular weight of about 84,000. That is the molecular weight range, determined by gel permeation chromatography was 84,000 +/- 1000 8/mole.

Once implanted at the site of a bone fracture, this polymer erodes through ahydrolysis mechanism to produce pentaerythritol dipropionate, 1,6-hexanediol and transcyclohexanedimethanol. These compounds are soluble in aqueous solution which assures complete removal of any polymer erosion residue from the implantation site.

One embodiment of the method utilizes the polyacetal previously described and enough PGE₂ to sssure delivery at a rate of about 1 ug/day over the course of 28 days.

The actual concentration of PGE₂ in the dosage form can range from about 0.01% to about 27- by weight. By "about 0.01% to about 2%" is meant that deviations at either extreme of the range of up to 507o can be tolerated in the dosage form prior to implantation.

SUBSTITUTE SHEET The amount of bioerodable polymer in the dosage form can range from about 99.99% to about 987, by weight of the components. By "about 99.99% to about 98%" is meant that minor deviations in the percentage of bioerodable polymer at either extreme of the range can be tolerated in the dosage form prior to implantation.

The desired delivery rate can be assured by first determining the jji vitro dissolution rate of the polymer in 0.15M phosphate buffered saline, pH 7.4 and adjusting the concentration of PGE₂ in the final product so that as the polymer bioerodes, the proper amount of PGE₂ is released. The volume of phosphate buffered saline utilized is based upon the total PGE₂ content of the dosage form. In testing of the low dose [what was amount per dosage form for low dose] 10 ml of potassium phosphate buffer was utilized. The high dose [what was amount per dosage form for high dose] utilized 75 ml of buffer. Samples were collected daily and the dissolved PGE₂ was quantified using routine analytical procedures.

One embodiment of the dosage form used in this novel method was prepared using the procedure described in example 2. This dosage form released approximately 807. of the PGE₂ within 10 days in an in vitro dissolution study.

As the following non-limiting examples show, the present invention has many advantages over any other known technology in that unexpedtely rapid bone knitting results from the implanation of this device at the site of a bone fracture.

SUBSTITUTESHEET EXAMPLES

Example 1:

Comparison ob Bone Growth and Repair Resulting from Infusion of Insulin Growth Factor 1 and

Prostaglandin E₂.

As the above results demonstrate, no change in bone formation was observed relative to the infusion of vehicle when IGF, was infused into the area requiring treatment. However, the infusion of PGE₂ resulted in an unexpected and increase in bone growth.

Example 2: Controlled delivery devices were fabricated by granulation of 1 g of spray dried poly(ortho ester) powder of the formula shown above (MW 84000 +/- 1000), with a PGE₂ in ethanol solution in a teflon jar. Devices with three different loadings of PGE₂ were fabricated to produce dosage forms which were nominally (A) 0.01%, (B) 0.1% and (C) 1.0% w/w PGE₂. The PGE₂ solution was slowly added to the polymer while stirring with a small spatula. Several ethanol rinses of the PGE₂ container were made and added to the granulation. The total amount of ethanol added to the polymer was enough to thoroughly wet the polymer (ca. 1-2 ml). After stirring with a spatula, the lid was loosely placed on the jar and the contents were vacuum dried for 18 hours.

SUBSTITUTE SHEET Devices were fabricated in two steps. First, a disk of PGE₂/ polymer material, weighing approximately 35 mg, was made using 1/4" flat punches in a Carver press at 500 psi. The disk was then positioned in the center of a die containing six cylindrical cut-outs. The die and pellet were sandwiched between two KAPTON sheets. This was placed between two heated plates (90°C) for 10 seconds before compression at 1 ton for 10-15 seconds. The die was immediately removed from the plates and placed on a cold steel plate. The devices were punched out of the die and stored at -80°C. Each device was a transparent disk with a diameter of 2 mm and a thickness of 1 mm and weighed about 4 mg. Placebo devices, that is those which contain only the polymer, were made by the same method except no E₂ was added. Table 1 shows the PGE₂ nominal content of each group of devices. Devices from groups A, B and C were tested for jji vitro dissolution properties. Five dosage forms from each group were placed in a bottle containing 0.15M phosphate buffered saline at pH 7.4. The lowest two dosages were tested using 75 ml of buffer. The bottles were capped and then rotated constantly for up to 14 days. A sample was removed each day and the PGE₂ released into the buffer was quantified using standard analytical procedures. The results of thes studies are shown in Table II.

Devices from groups A, B, C and placebo pellets were tested in vivo in a rat model. An untreated control group was maintained as a further control. Male Sprague-Dawley rats weighing 250 g (Taconic Farms, NY) were divided so that four rats

H ET were in each of the four treatment groups . The animals were anesthetized intraperitoneally using ketamine hydrochloride (KETASET, Aveco, 80 mg/kg). A longitudinal incision was made along the medial aspect of the proximal tibia down to the periosteum. Under saline irrigation of 2 mm hole was drilled through the cortex approximately 2 mm inferior to the epiphyseal growth plate using a #8 carbide plain round excavating bur with a high speed dental drill. The devices were placed within the marrow cavity and the incisins closed. The animals recovered without incident and within 24 hours following surgery demonstrated normal locomotion and grooming behavior.

Eight days following surgery animals were sacrificed using a C0₂ inhalation chamber and the tibia removed and fixed in 70%. ethanol for histological processing and methacrylate embedding. Coronal six micron thick sections were cut using a microtome and stained with toluidine blue. Tissue sections were analyzed histomorphometrically.

Table III lists the cortical bone thickness and percent cancellous bone found for the difference groups in this trial. This histomorphometic data provides evidence for a dose-related increase in metaphyseal bone formed as a result of prostaglandin treatment. Bond volume was 8.66% for the placebo treated group and was significantly increased (p,0.05) threefold with the group A devices. Also, the rate treated with group A devices showed a significant increase in cortical bone thickness.

SUBSTITUTE SHEET Results from previous studies indicate that control rats with holes drilled in their tibia do not show growth statistically different from untreated controls.

TITUTE SHEET

Claims

WHAT IS CLAIMED IS:

1. A method of stimulating bone growth comprising the administration of PGE,, PGE₂, ^PGF2α' ^β-^{estradl01 or} their salt in a controlled release manner, from a rod shaped, rigid, solid, biodegradable polymer, at a site at which bone growth stimulation is desired.

2. A method of stimulating bone growth of Claim 1, wherein the site of desired stimulation is selected from the group consisting of bone fractures and osteoporosis.

3. The method of stimulating bone growth of Claim 2, wherein the site of desired stimulation is at a bone fracture.

4. The method of stimulating bone growth of Claim 1, wherein the amount of free PGE,, PGE₂, PGF₂ , or β-estradiol administered to the site where bone growth stimulation is desired is about 0.01 ug/day to about 1 g/day.

5. An implantable controlled release dosage form, shaped for ready implantation in or near a bone in need of therapy, consisting essentially of:

(a) a rigid, solid, bioerodible polymer selected from a poly(ortho ester) or a polyacetal, which upon bioerosion, produces water soluble compounds which do not leave a

SUBSTITUTE SHEET residue at the site of implantation in the subject undergoing treatment; and implantation therewith,

(b) a therapeutically effective amount of PGE₁, GE₂,

PGF_2α, β-estradiol or their salt.

6. The controlled release dosage form of Claim 5, wherein organic and inorganic compounds are added to the polymer and drug mixture to modulate the bioerosion process.

7. The controlled release dosage form or Claim 5, wherein the bioerodible polymer release PGE₁, PGE₂, ^p F_2a or their salt in a controlled manner, at the site of implantation, whereby these compounds are available for therapeutic stimulation of bone growth.

8. The controlled release dosage form of Claim 5 wherein rigid, solid, bioerodible polymer is a poly(ortho ester).

9. The controlled release dosage form of Claim 5 which consists essentially of about 0.01% to about 2% PGE₂ by weight and between about 99.99% and about 98% of polymer.

SUBSTITUTE SHEET