Controlled release of macromolecular polypeptides

Abstract: An active agent delivery system for the controlled administration of macromolecular polypeptides which comprises a micro-suspension of water-soluble components in a polylactide matrix.

Description: This invention relates to an active agent delivery system for administering macromolecular polypeptide active agents having molecular weights of about 10,000 or greater, particularly interferons, at a controlled rate for a prolonged period of time. The traditional and most widely used method of administration of therapeutic agents is by the oral route. However, in the case of large polypeptides, such delivery is not feasible due to the hydrolysis of the peptides by digestive enzymes. The methods most commonly used for administration of polypeptide therapeutic agents are by repeated injection, intramuscular (IM), subcutaneous (SC) or intravenous (IV) infusion. These methods are acceptable in situations where a very limited number of injections are required, but are undesirable for chronic administration (for example as with insulin therapy). The nature of many of the diseases, disorders and conditions susceptible to improvement by polypeptide administration is chronic rather than acute, thus necessitating frequent injections over a prolonged period of time. There is, therefore, a need for an efficacious and economical delivery system for large polypeptide agents, Biodegradable polymer matrices formed from polylactic acid or copolymers of polylactic acid with other comonomers such as polyglycolic acid have been used as sustained release delivery systems for a variety of active agents, due to their ability to biodegrade in situ . See, for example, U.S. Patent Nos. 4,293,539, and 4,419,340. The use of these polymers in implants for delivery of several therapeutic agents has been disclosed in scientific publications and in the patent literature. See, for example, Anderson, L.C. et al, (1976), "An injectable sustained release fertility control system", Contraception 13 : 375-384; Beck et al. (1979) "New long-acting injectable microcapsule contraceptive system", Am . J . Obstet . Gynecol . 140 : 799-806; Yolles et al. (1978) "Timed release depot for anti-cancer agents II", Acta Pharm. Svec . 15 : 382-388, US 3,773,919, and U.S. Patent Application Serial No. 699,715 filed February 8, 1985. Sustained delivery of peptides from poly(lactide-co-glycolide) systems has been reported by Kent et al. (1982), " In vivo controlled release of an LHRH analog from injected polymeric microcapsules", Contracept. Deliv . Syst . 3 : 58; by Sanders et al. (1984), "Controlled release of a luteinizing hormone-releasing hormone analogue from poly (d,l-lactide-co-glycolide)-microspheres" (see also European Patent No. 0052510), J . Pharmaceut. Sci . 73 : 1294-1297, by T. Chang, "Biodegradeable semipermeable microcapsules containing enzymes, hormones, vaccines and other biologicals". J . Bioengineering, 1 , 25-32 (1976), and in EPO Application No. 82300416.3, filed January 27, 1982 (now European Patent No. 0058481). Also, EP 134 318 describes the controlled release of insulin, via the formation of aqueous channels, from a biodegradable polymer matrix composition. However, the delivery of large polypeptides from polylactide matrices has been very difficult to achieve, for reasons that will be further discussed. Of the publications cited above, only the latter two disclose devices containing polypeptides having molecular weights of 2500 or greater. Polylactide and poly(lactide-co-glycolide) polymers and copolymers (referred to generically hereinafter as polylactide or PLGA polymers) are not soluble in water. In contrast, most polypeptides are soluble in water but not in organic solvents. For this reason, the preparation of polylactide devices in which polypeptide particles are dispersed has, until now, generally followed one of two basic techniques. One technique involves mixing of the components with the polylactide in the molten state followed by heat extrusion, heat pressing, or casting. The second technique involves the creation of a solution/suspension of the polymer and polypeptide in an organic solvent, which is then pour-cast into a film or slab and the solvent evaporated, The latter method usually requires extensive or rapid stirring of the solution/suspension in order to achieve an acceptable degree of uniformity of the polypeptide particles and homogeneity of the polypeptide/polylactide matrix upon solidification. Evaporation of the solvent takes place over several hours to several days unless the film or slab is dried under vacuum, in which case bubbles are invariably created as the solid dries. Additionally, polylactide formulations prepared in this way are not sufficiently uniform for most therapeutic applications; due to coalescence of the water-soluble particle phase, the polypeptide is unevenly distributed within the polylactide as large aggregates of particles. Therefore, formulations prepared in this way must be submitted to further homogenization procedures such as grinding the formulation to a powder and reforming it under heat, or compressing or extruding the formulation under heat. The temperature required for for these manipulations is usually at least 70° C. It is also known to make injectable microcapsules of drug in polylactide. Such microcapsules can be prepared by basic techniques such as that set out in U.S. Patent No. 3,773,919, and in U.S. application Serial No. 699,715, and European Patent No. 0052510. The latter method involves dissolving the polymer in a halogenated hydrocarbon solvent, dispersing the aqueous polypeptide containing solution by rapid stirring in the polymer-solvent solution, and adding a non-solvent coacervation agent which causes the polymeric excipient to precipitate out of the halogenated hydrocarbon solvent onto the dispersed polypeptide containing water droplets, thereby encapsulating the polypeptide. The resulting microcapsules are then dried by repeated organic solvent washings. However, large polypeptides are particularly susceptible to physical and chemical denaturation and consequent loss of biological potency from exposure to excessive heat, solvents, and shear forces. For this reason, incorporation of large polypeptides in polylactide polymers has, until now, required either compromise in the degree of uniformity of the polypeptide/polymer dispersion, or has resulted in substantial loss of the biological potency of the polypeptide, or both. The resultant formulations are generally nonuniform dispersions containing irregularly sized large particles of polypeptide of reduced potency. The incorporation of large and irregular particles of polypeptide causes an uneven rate of drug delivery, and tends to exacerbate the multiphasic release profiles generally associated with polylactide pharmaceutical preparations. Preparation of more homogenous monolithic formulations by known techniques, such as mixing of the molten components, grinding, and heat homogenation techniques such as compression and extrusion may result in a substantial, often nearly complete loss of biological activity of the polypeptide. For example, a PLGA/interferon formulation formed by heated mixing and extrusion under mild conditions retains less than 1% of the original biological activity of the interferon. (See Example 7, below.) To compensate for the loss in biological activity during manufacturing processes of this type, a large excess of polypeptide must be incorporated in the formulation. A further disadvantage of formulations which contain denatured polypeptides is the increased immunogenicity which they exhibit. Antibody formation in response to the denatured polypeptide may partially or entirely contravene the desired therapeutic effect. Accordingly, there is a need for a homogeneous polylactide device which provides controlled and regular delivery of macromolecular polypeptides and can be manufactured without significant loss of biological activity. The present invention provides a method for preparing an active agent delivery system for the controlled administration of a water soluble macromolecular polypeptide to a mammal. The system comprises a polymeric matrix comprising not more than about 30 percent by weight of particles of denaturable macromolecular polypeptide of molecular weight greater than 10,000 and other optional water-soluble components dispersed in a polylactide matrix, wherein substantially all of the particles of polypeptide and other water-soluble components have diameters of 10 µm or less and are uniformly and discretely dispersed throughout the matrix, and wherein the polypeptide retains at least about 50 percent of the biological activity which it possessed prior to manufacture of the matrix. The method comprises preparing a microsuspension of the polypeptide, and other water-soluble components, in the polylactide solution, and spray-casting or atomizing the microsuspension. This device provides an economical and reliable method of delivering controlled and regular quantities of biologically active macromolecular polypeptides to body sites which are capable of making available intracellular and or extracellular fluids for transfer into the device. The system can be designed to deliver the active agent at an appropriate rate over prolonged periods of time ranging from less than one day to several months. Generally, active agent release periods of about one week to three months are contemplated. An important advantage of this controlled release device resides in the fact that it can be manufactured with only minor loss of biological activity of the polypeptide active agent. Maintenance of high biological activity permits the device to be manufactured to contain relatively low initial amounts of the polypeptide. As a result of maintaining high biological activity of the peptide during manufacture, several further advantages are achieved. First, there is a significant economic advantage to the manufacturer with respect to the cost of active agent incorporated in each dosage form or delivery system. Second, due to the relatively low percentage of polypeptide and other water-soluble components in the device, the contribution of these components to the hydration of the system in vivo is minimized, thereby providing a more constant rate of polypeptide release throughout the entire operational life of the device than can be obtained with previously known biodegradeable systems. Third, the absence of significant quantities of denatured polypeptide reduces the likelihood of undesirable immune responses at the site of polypeptide delivery. A further advantage of this device is that it can be manufactured with little loss of active ingredient. This of course is useful in reducing wastage of active ingredient. Initially the manufacture obtains 80% incorporation of active ingredient starting material into the device, preferably at least 90%, most preferably substantially 100% incorporation. Another important advantage of the method is that is produces a controlled release device with a novel physical structure of the polymer/polypeptide matrix. The matrix comprises a very fine dispersion, or micro-suspension, of water soluble components in a polylactide polymer, wherein substantially all of the particles of active agent and any other optionally present water soluble components have diameters of 10 µm or less. These particles are uniformly and discretely dispersed throughout the polymer, providing an essentially homogeneous and monolithic device. As with previously known systems, the biologically active polypeptide is released through a combination of diffusion and dissolution mechanisms as the device hydrates and subsequently erodes. However, unlike known polymeric matrix systems which deliver macromolecules, the system produced by this invention does not rely on the formation of aqueous channels, or macropores, in the matrix for release of the macromolecules from the system. The requirement of macropore formation for drug release to occur is known to result in a triphasic release profile characterized by a middle quiescent phase during which little or no drug is released. There may also be a quiescent, or dead period before the initial phase of drug release. In contrast, because the polypeptide and other water soluble components of this invention are present as very small and discrete particles within the polylactide matrix, aqueous channels are not formed, if at all, until relatively late in the release period. As a result, a very regular release profile is achieved which can be made to begin with very little initial lag time, and which is continuous throughout the life of the system. An appropriately sized and shaped device of the above description can be used for administering a macromolecular polypeptide active agent at a body site which is capable of making available its intracellular and/or extracellular fluids for absorption by the implant. FIGURE I is a graph of the data obtained from the test described in Example 3, and shows the release profiles of β-interferon from active agent delivery systems implanted subcutaneously in mice over a period of 60 to 100 days. The systems were prepared according to the invention as described in Examples 1 and 2. Definitions The term "biologically active macromolecular polypeptide" refers to any polypeptide having a molecular weight of not less than about 10,000 daltons, which possesses useful biological activity when administered to a mammal. The phrase "wherein the polypeptide retains at least about 50% of its biological activity" means that at least about 50% of the biological activity potential of the polypeptide will remain at completion of manufacture, as determined within the accuracy of a biological assay for the particular polypeptide such as the one described in Example 5. Generally, the assay will involve spiking the polypeptide loading stock with a known concentration of radioactively labelled polypeptide, extracting the polypeptide from the manufactured system under mild conditions, and determining both the relative radioactivity (counts per minute per ml), and the relative units/ml biological activity, of the loading stock and the extracted polypeptide in a standard biological assay for the polypeptide. The biological assay is performed against a reference standard in serial dilution test wells of the polypeptide samples to be assayed. An arbitrary endpoint is set for scoring the test wells, and the same endpoint is used in scoring the reference samples. The activity of the interferon samples is calculated based on the log 10 of the units/ml biological activity of the loading stock equivalent for each extracted sample. Systems produced by this invention will demonstrate relative log 10 polypeptide activity values which are one/half, or greater, than the log 10 units/ml of the corresponding polypeptide loading stock. The preferred embodiments of this invention retain at least about 70 % of the biological potential of the polypeptide after manufacture, more preferably at least 90%, most preferably substantially all of the biological potential. The term "substantially all of the particles of polypeptide and other water-soluble components" refers to at a quantity of at least about 75 % of the particles of components so identified, more suitably at least about 90%. The term "water-soluble" is used herein to refer to macromolecular polypeptides and other optional pharmaceutically acceptable components which are at least "very slightly soluble" by the definition given in the United States Pharmacopeia , XX , page 1121, i.e. having water solubilities of at least 0.1-1.0 mg/ml. The term "micro-suspension" is used herein to describe particles of polypeptide and other water soluble solid components, substantially all of which have diameters of 10 µm or less, which are substantially uniformly and discretely dispersed throughout the polymer. The term "uniformly and discretely dispersed" is used to indicate that the particles are not touching each other, but rather are individually surrounded by polymer, and are approximately equi-distantly spaced. Determination of the size and distribution of the particles of polypeptide and other water-soluble components can be made by a standard microscopic examination such as that described in Example 4, below. Preferably, substantially all of the particles will have diameters of 5 µm or less, and more preferably, 1 µm or less. The term "polylactide" is used herein in a generic sense to describe both homopolymers and copolymers derived from alpha-hydroxycarboxylic acids, particularly α-hydroxyacetic (lactic) and α-hydroxypropionic acid (glycolic) acids. They are usually prepared from the cyclic esters of lactic acids. The present invention resides in the creation of a homogeneous matrix of a polylactide in which is incorporated a substantially uniform micro-suspension of a biologically active macromolecular polypeptide. The matrix releases the biologically active polypeptide when placed at a body site which can make available is intracellular and/or extracellular fluid for transfer into the device. As the matrix becomes hydrated, the polypeptide is released by diffusion and erosion mechanisms. Because the polypeptides are water-soluble, the rate of release is governed by the rates of hydration and polymer erosion of the device. Methods of preparing polylactides are well documented in the scientific and patent literature. The following patents provide detailed descriptions of suitable polylactides, their physical properties, and methods of preparing them: U.S. 3,773,919, U.S. 4,293,539, U.S. 3,435,008, U.S. 3,442,871, U.S. 3,468,853, U.S. 3,597,450, U.S. 3,781,349, U.S. 3,736,646 and European Patent No. 0052510. The macromolecular polypeptides which may be incorporated in the device produced by this invention are biologically active molecules having molecular weights greater than about 10,000, most preferably greater than about 15,000. The choice of polypeptides which can be delivered in accordance with the practice of this invention is limited only by the requirement that they be at least very slightly soluble in an aqueous physiological media such as plasma, interstitial fluid, and the intra and extracellular fluids of the subcutaneous space and mucosal tissues. The term "very slightly soluble" refers to a water-solubility of at least about 0.1-1.0 mg/ml, as defined hereinabove. A particularly preferred class of polypeptides are the naturally occurring and synthetic interferons. Interferons are polypeptides having monomer molecular weights in the range of about 15,000 to about 28,000. They are proteins which are synthesized by mammalian cells in response to viral infection, immune stimulation and other factors. They are presently designated as members of one of three major classes: alpha or leukocyte interferon (IFN-α), beta or fibroblast interferon (IFN-β), and gamma or immune interferon (IFN-γ). Their biological properties include antiviral, anti-proliferative and immunomodulating activities, which have led to their clinical use as therapeutic agents for the treatment of viral infections and malignancies. Interferons can be obtained from natural sources such as leukocytes, lymphoblastoid cells in continuous suspension or culture, and fibroblast cultures. T lymphocytes can be stimulated to produce gamma interferon. β-interferon is derived from mammalian cells such as fibroblast cells. As used herein, "β-interferon" or "IFN-β" includes β-interferon derived both from natural sources, including human, bovine, canine, feline, porcine and equine, and by recombinant DNA techniques. It also includes modified forms of β-interferon; e.g., by glycosylation, methylation, substitution and/or deletion of a limited number of amino acids. As used herein, HulFN-β refers to human β-interferon, and rHulFN-β refers to HulFN-β produced using recombinant techniques. IFN-β ser-17 refers to β-interferon in which the seventeenth amino acid has been replaced with serine. Interferon concentrations are commonly expressed as standard "units" which are internationally accepted and documented, and relate to the potency of a given quantity of interferon to inhibit virus replication under standard conditions. In addition to incorporating one or more biologically active macromolecular polypeptides, the controlled release device of this invention may contain other water soluble, pharmaceutically acceptable components. The optional water-soluble components which may be incorporated in the polylactide matrix are present as particles having diameters of about 10 µm or less. If present, they are intimately mixed with the macromolecular polypeptides, and are uniformly and discretely dispersed throughout the polymer. Most macromolecular polypeptides benefit from the presence of small quantities of stabilizers, buffers, salts and the like. Water-soluble components which may be useful in the practice of this invention include, but are not limited to other active agents, proteins or other polypeptides, stabilizers, carbohydrates, buffers, salts, surfactants and plasticizers. Examples of suitable stabilizers include human serum albumin (HSA), gelatin, dextrose, other carbohydrates. Examples of other carbohydrates suitable for incorporation in this invention include sucrose, maltose, mannose, glucose, fructose, lactose, sorbitol and glycerol. Suitable surfactants include Tween (e.g. Tween-20, Tween-80), Pluronic® polyols such as Pluronic® L101, L121 and F127 (see standard works such as Merck Index Tenth Edition for further details of these well known surfactants). Among the suitable plasticizers are the polyethylene glycols, glycerides and ethylcellulose. The relative proportions of macromolecular polypeptide and other-water soluble components to polylactide and water-insoluble components within the matrix can be varied depending on the polypeptide to be administered and the desired rate and duration of release. The macromolecular active agent and other water-soluble components may comprise up to about 30 weight percent of the system. The precise amount will depend on such factors as the potency of the particular active agent, its physiochemical and pharmacokinetic behaviour, its stability and the desired duration of release. A preferred composition for the polylactide matrix comprises, by weight: (a) 80 to 99.9999 % polylactide; and (b) 0.0001 to 20 % biologically active macromolecular polypeptide and other optional water-soluble components. For very active polypeptides, the total amount of polypeptide and other water-soluble components may be as low as 10%, 5%, 2% or less of the total weight of the matrix. The present invention is well-suited to the controlled delivery of interferons. The amount of interferon incorporated in the polylactide matrix will preferably be 20%, or less, depending on the particular interferon and the other factors listed above. A presently preferred composition comprises, by weight: (a) 90 to 99.999 % polylactide; and (b) 0.001 to 2 % HulFN-β, and may include up to about 10% of other water-soluble components. A more preferred composition comprises, by weight: (a) 95 to 99.9 percent polylactide; (b) 0.01 to 0.1 percent HulFN-β, and may include up to about 5 % of other water-soluble components. A particularly preferred composition comprises, by weight: (a) 97.47 percent poly(lactide-co-glycolide) having a molar ratio of 50:50 and an intrinsic viscosity of about 0.64 dl/g; (b) 0.03 percent HulFN-β; (c) 1.25 percent human serum albumin; and (d) 1.25 percent dextrose. The preferred interferon for incorporation in the foregoing systems is rHulFN-β ser17 . Methods of Preparation The delivery systems of this invention may be fabricated by any method which achieves the desired micro-suspension conformation and substantially maintains the biological activity of the macromolecular polypeptide. A preferred method involves spray-casting of a micro-suspension of the polypeptide in a solution of the polylactide. The skilled chemist will comprehend various methods by which the micro-suspension can be made. Two novel and useful methods are described below. (The skilled man will appreciate that solvents other than acetone and methylene dichloride may be used, provided the protein is compatible with, and insoluble in, the solvent.) Acetone Method An aqueous, buffered solution of the macromolecular polypeptide and other optional water-soluble components buffer is added to a solution of the chosen polylactide in acetone at room temperature. The resulting mixture is vortexed at high speed using a standard laboratory vortex mixer for approximately 5 to 120, preferably about 10, seconds. A precipitate of the polymer, polypeptide, and other components is formed which is then centrifuged for about 0.5 to 30 minutes, preferably about 10 minutes, at 500 to 1000, preferably 700 X g . The resulting supernatant of acetone and water is removed, additional acetone added, and the mixture vortexed at high speed until the polymer, for example PLGA, in the pellet is dissolved, leaving a micro-suspension of polypeptide and other water-soluble components in the solution of polymer in acetone. Methylene Dichloride Method An aqueous, buffered solution of the polypeptide and other optional water-soluble components is added to a solution of the chosen polylactide in methylene dichloride. The resulting mixture is vortexed for approximately 10 to 180 seconds, preferably about 60 seconds, at high speed, until a white emulsion is formed. The emulsion is immediately transferred to an airbrush or other suitable spray device and spray cast as described below. Formation of the Active Agent Delivery Systems The active agent delivery systems produced by this invention are formed so that the final solid polypeptide/polylactide matrix product possesses the required micro-suspension morphology in which substantially all of the particles of polypeptide and other water-soluble components have diameters of 10µ or less and are uniformly and discretely dispersed throughout the matrix. To assure that the liquid micro-suspension of water-soluble components in the polymer solution does not coalesce into a suspension of larger particles upon solidification of the formulation, it is preferable to promptly spray-cast the micro-suspension onto a non-stick surface with an airbrush or other suitable device using appropriate conditions. The airbrush is preferably held about 10 to 15 cm from the surface of the sheet and the film sprayed with a constant motion to achieve an even film. Suitable non-stick surfaces include polypropylene, teflon, nylon, polyethylene or derivatives thereof, and other materials with similar non-stick properties. Polypropylene, teflon and polyethylene are preferred. The spray-cast film can be made as thin as about 5 µm and as thick as 1000 µm. For films thicker than about 100 µm it is preferable to allow some time for drying between repeated spray-castings of layers. Thinner films (about 10 to 50 µm) are preferred when it is desirable to minimize the exposure of the polypeptide to the organic solvent. Generally, the resulting film should be allowed to dry completely before being configured into the final controlled release device or system. Depending on the thickness of the film, the drying time to achieve complete dryness will vary from less than one hour to about three days, and can be shortened if desired by drying under vacuum after the matrix has solidified to the point where bubbles will not be caused. For many polypeptides, parenteral injection is a preferred route of administration. The polypeptide/polylactide matrix formulation can be prepared in an injectable form by atomizing the liquid micro-suspension and drying the resulting micro-particles in a counter-current or vortex of air or inert gas. The resulting particles can be injected directly, or can be incorporated in a compatible and pharmaceutically acceptable injectable solution or suspension. The controlled delivery systems may be structurally reinforced with an inert, pharmaceutically acceptable material such as a fine silk mesh, teflon mesh or other surgically inert material. It is especially advantageous to incorporate a reinforcement material when it is anticipated that the controlled release device will need to be recovered from its active delivery site. Reinforced devices may be made by spraying the polypeptide/polylactide micro-suspension onto the reinforcement material, which is preferably resting on a non-stick surface. The film is then allowed to dry briefly, and can be turned over, and sprayed on the other side. This procedure is repeated until a film of the desired thickness is achieved. Preferably, the texture of the reinforcement material will be completely covered by a smooth layer of the polymer. The polymeric film obtained by spray-casting as described above can be configured into any solid article suitable for the intended site of use. For example, the film can be cut into pieces of known dimensions and implanted subcutaneously as single segments. Alternatively, the film can be rolled into a cylindrical device of desired dimensions. Multiple layers of film can be laminated and die-cut to create devices of virtually any size and shape. Integrity of the layers can be assured by light spraying or brushing between lamination of layers with a suitable solvent for the polymer or exposure to solvent vapor. The controlled release devices can be designed to deliver the biologically active macromolecular polypeptide, and any accompanying active agents, at a controlled rate over a prolonged period of time ranging from less than one day to several months. Examples of devices which delivered therapeutically useful levels of β-interferon subcutaneously over a period of 60 to 100 days are described in Examples 1 and 2 and shown in Figure I. The actual rate and duration of release can be varied within the practice of this invention by the choice of polylactide polymer (e.g. choice of monomer or comonomers, molar ratio and intrinsic viscosity) or copolymer, by the shape and configuration of the device (e.g. flat, rolled, single layer or multiple layer), and to a lesser extent, by the amount of active agent which is incorporated. The amount of active agent incorporated in the device can vary between 0.0001 and 30 percent, by weight, of the polymeric system. The optimal amount for any given system will depend on the potency of the agent, the desired physiologic effect, the intended length of treatment, and the rate of active agent release. Preferably, the devices contain about 0.0001 to 20 percent. by weight, of the macromolecular polypeptide. The size of the device will likewise depend on the amount of active agent which it contains, its release rate, and the intended duration of treatment. For example, if it is known that a particular polypeptide/polylactide formulation releases the polypeptide at an average rate of 10 6 units per day, and the desired duration of treatment is 60 days, the device would require a loading of at least 6 x 10 7 units of polypeptide. Based on the weight percent polypeptide in the system, the required size of the device can be calculated. The following preparations and examples are provided to further illustrate the practice of this invention, and are not intended to in any way limit its scope. EXAMPLE I Preparation of Controlled Release Devices Containing Interferon (Acetone Method) A. Preparation of IFN/PLGA Micro-suspension One gram of D,L-PLGA (molar ratio 50:50, inherent viscosity 0.64 dl/g) was dissolved in 5 ml acetone at room temperature. 0.3 mg of recombinant HulFN-β in 1 ml of buffer (containing 12.5 mg HSA and 12.5 mg dextrose) was added to the PLGA in acetone and the resulting mixture was vortexed at high speed for approximately 30 seconds. The precipitate of PLGA, HSA, IFN and possibly dextrose which formed was then centrifuged for 10 minutes at 700 X g . The supernatant of acetone and water was removed with a pipet and the residual liquid removed with a cotton swab. Ten ml acetone was added, and the mixture was vortexed at high speed until the PLGA in the pellet was dissolved, leaving a micro-suspension of HulFN-β, HSA and dextrose in a solution of PLGA in acetone. B. Spray-Casting of the IFN/PLGA Micro-suspension The resulting IFN/PLGA micro-suspension, obtained as described in paragraph A, was sprayed with an airbrush, using compressed air at 1 Kg cm -2 onto a clean polyethylene sheet. The airbrush was held 10-15 cm from the surface of the sheet and the film sprayed with a constant motion to achieve an even film of the PLGA formulation which was approximately 50 µm thick. C. Reinforcement of Film Using IFN/PLGA micro-suspension from paragraph A, a spray-cast film with silk reinforcement was prepared as follows: Fine woven silk mesh was stretched on a frame and the stretched portion brushed with a solution of 100 mg/ml PLGA (molar ratio 50:50, intrinsic viscosity 0.64) in acetone. The wet mesh was allowed to dry, and then brushed with repeated applications of PLGA solution until the pores in the silk mesh were completely filled. The mesh was then dried, placed on a polyethylene sheet, and spray-cast with the IFN/PLGA micro-suspension. After drying for one hour, the coated mesh was turned over, coated side down, and again sprayed with the IFN/PLGA micro-suspension, applying a layer of polymer about 100 µm thick. After drying for another hour, the previously coated side was again sprayed, allowed to dry, turned over, and the second side sprayed again. The resulting film had a thickness of 300 µm. D. The films obtained in paragraphs B and C were stored at room temperature for 18 hours. They were then removed from the polyethylene sheet and dried at room temperature for three days. E. Device Configuration Using spray-cast film obtained as described in paragraphs A-D, above, controlled release devices were configured as follows: a. Flat film segments, 1 × 2 cm, were cut from the non-reinforced film. b. Flat film segments, 1 × 2 cm, were cut from the reinforced film. c. Flat film segments, 3 × 5 cm, were cut from non-reinforced film, were rolled on an 18 gauge wire and the film secured by a very light application of acetone with a cotton swab to the final 5 mm length, or by exposure to acetone vapor. The wire was removed and the rolls sliced into lengths of 5 or 10 mm. d. Flat film segments, 3 × 5 cm, were cut from reinforced film, were rolled on an 18 gauge wire and the film secured by a very light application of acetone with a cotton swab to the final 5 mm length, or by exposure to acetone vapor. The wire was removed and the rolls sliced into lengths of 5 or 10 mm. The release profiles of these devices when implanted subcutaneously in mice over a period of 100 days are shown and identified in Figure I as devices 1, 2, and 3 for configurations a, b, and c respectively. EXAMPLE 2 Preparation of Controlled Release Devices Containing Interferon (Methylene Dichloride Method) One gram of D,L-PLGA (molar ratio 50:50, intrinsic viscosity 0.64 dl/g) was dissolved in 4 ml methylene dichloride. 0.3 mg of recombinant HulFN-β in 1 ml of buffer containing 12.5 mg/ml human serum albumin (HSA) and 12.5 mg/ml dextrose was added to the dissolved PLGA solution. The resulting mixture was vortexed for approximately 60 seconds at high speed until a white emulsion was formed. The emulsion was immediately transferred to an airbrush and sprayed onto a polyethylene film, and dried in the same manner as described in Example 1, paragraph D. Controlled release devices were configured by rolling 3 cm x 5 cm film segments on an 18 gauge wire, securing the end of the roll by exposure to acetone, removal of the wire, and slicing of each roll into 5 and 10 mm lengths. The release profile of these devices when implanted subcutaneously in mice over a period of 60-100 days is shown as device 4 in Figure I. EXAMPLE 4 Determination of Particle Size and Distribution PLGA/IFN films prepared as described in Examples 1 and 2, above, were analyzed to determine the particle size of the interferon and other macromolecules (human serum albumin and dextrose) in each formulation, according to the following procedures: A. PLGA/IFN films prepared as described in Example 1 One gram of D,L-PLGA (molar ratio 50:50, intrinsic viscosity 0.64 dl/g) was dissolved in 5 ml acetone at room temperature. 0.3 mg of recombinant HulFN-β in 1 ml of buffer containing 12.5 mg HSA and 12.5 mg dextrose was added to the PLGA in acetone and the mixture was vortexed at high speed for approximately 10 seconds. The precipitate of PLGA, HSA, IFN and possibly dextrose which formed was then centrifuged for 10 minutes at 700 X g . The supematant of acetone and water was removed with a pipet and the residual liquid removed with a cotton swab. Ten ml acetone were added, and the resulting mixture vortexed at high speed until the PLGA in the pellet was dissolved, leaving an IFN, HSA, dextrose precipitate suspended in PLGA dissolved in acetone. A drop of the suspension was viewed under a polarizing light microscope on a glass slide with cover slip at 100X magnification using an ocular reticle with 10 micrometer divisions. The particle sizes of the solid macromolecular components (IFN, HSA, dextrose) suspended in the PLGA/acetone solution ranged from less than or equal to the limit of detection (approximately 100 to 500 nanometers) to 100 µm. Particles having diameters of greater than 10 µm were less than 10 % of the total number of particles, and most of the particles had diameters of less than 1 µm. Less than 10 % of the visible particles could be observed to be touching at least one other particle. B. PLGA/IFN films prepared as described in Example 2 A drop of the PLGA/IFN micro-suspension prepared according the the method described in Example 2 above was viewed under a light microscope on a glass slide with cover slip at 100X magnification using an ocular reticle with 10 micrometer divisions. No particles were observed at 100X magnification, indicating that all of the IFN and HSA had particle sizes of less than or equal to the limit of detection (100 to 500 nanometers). C. Calculation of Interferon Specific Biological Activity The radioactivity of three 1 to 50 µl aliquots of each undiluted interferon sample is determined by counting in a Packard gamma counter. From the result in counts per minute (CPM), the counts per unit volume is determined (CPM/ml). The IFN activity (IFN units/ml) of each sample, determined according to the method described in paragraphs A and B, above, is divided by the CPM/ml value for the sample, giving the activity of the IFN in units/CPM. The units/CPM value for each sample obtained by extraction from a manufactured polylactide system is divided by the units/CPM value for the corresponding starting stock interferon material (loading stock IFN) used to make the manufactured polylactide/interferon systems, to give the ratio of specific activity of extracted interferon to the specific activity of loading stock IFN. The ratio so obtained is multiplied by the IFN units/ml value for the loading stock IFN, which gives the loading stock IFN units/ml equivalent of the extracted IFN sample. The log 10 of the loading stock IFN units/ml equivalent for each extracted sample is termed the relative log 10 IFN activity (RLIA). RLIA values for each group of samples tested are averaged and compared to the log 10 IFN units/ml value of the appropriate loading stock. Additional accuracy can be gained by a linear regression analysis of RLIA values obtained from a series of systems which have been implanted in a test animal, such as mice, and serially recovered at several intervals over the test period, e.g one month. The Y-intercept of the line determined from a graph of RLIA values (Y axis) versus days of implantation (X axis) indicates the activity of the interferon in the manufactured systems prior to implantation. D. Results The controlled release systems demonstrate RLIA values following manufacture, but prior to in vivo application, which are one/half, or more, of the log 10 IFN units/ml of the corresponding polypeptide loading stock. Interferon/polylactide systems prepared as described in Examples 1 and 2, when assayed as described in this example, show essentially no loss of biological activity of the incorporated interferon; that is, the average RLIA values after manufacture but before implantation are essentially indistinguishable from the log 10 IFN units/ml of the IFN loading stock from which they were prepared.

Claims: A method for producing an active agent delivery system for the controlled administration of a macromolecular polypeptide to a mammal, which system comprises a polymeric matrix comprising not more than about 30 percent by weight of particles of denaturable macromolecular polypeptide of a molecular weight greater than 10,000 and other optional water-soluble components, dispersed in a polyactide, wherein substantially all of the particles of polypeptide and other water-soluble components have diameters of 10 µm or less and are uniformly and discretely dispersed throughout the matrix, and wherein the polypeptide retains at least about 50 percent of the biological activity which it possessed prior to manufacture of the matrix; said method comprising preparing a microsuspension of the polypeptide, and other optional water-soluble components, in the polylactide solution, and spray-casting or atomizing the micro-suspension. A method according to claim 1 in which the polypeptide is selected from cytokines, lymphokines, monokines and interferons. A method according to claim 2 in which the polypeptide is interleukin-1, or interleukin-2. A method according to claim 2 in which the polypeptide is a beta interferon. A method according to claim 1 in which the polypeptide is an immune stimulator or an immune depressant. A method according to claim 1 in which the polypeptide is a plasminogen activator. A method according to claim 1 in which the polypeptide is a growth hormone. A method according to claim 7 in which the polypeptide is bovine growth hormone. A method according to claim any one of the preceding claims, in which the system incorporates a biocompatible inert reinforcement material. A method of any one of the preceding claims in which the polylactide is a poly(lactide-co-glycolide) copolymer having a molar ratio of lactide to glycolide units of between about 100:0 and 30:70.

Inventors: EPPSTEIN DEBORAH ANN, SCHRYVER BRIAN BLOOR, EPPSTEIN, DEBORAH ANN, SCHRYVER, BRIAN BLOOR
Applicants: SYNTEX LLC, SYNTEX (U.S.A.) LLC
Application year: 1987
Main classification: A61K9
IPC codes: A61K47, A61K38, A61K9