Improved porous particles for drug delivery to the pulmonary system, and methods for their synthesis and administration are provided. In a preferred embodiment, the porous particles are made of a biodegradable material and have a mass density less than 0.4 g/cm.sup.3/. The particles may be formed of biodegradable materials such as biodegradable polymers. For example, the particles may be formed of a functionalized polyester graft copolymer consisting of a linear a-hydroxy-acid polyester backbone having at least one amino acid group incorporated therein and at least one poly(amino acid) side chain extending from an amino acid group in the polyester backbone. In one embodiment, porous particles having a relatively large mean diameter, for example greater than 5 .mu.m, can be used for enhanced delivery of a therapeutic agent to the alveolar region of the lung. The porous particles incorporating a therapeutic agent may be effectively aerosolized for administration to the respiratory tract to permit systemic or local delivery of wide variety of therapeutic agents.

Description of the Invention

SUMMARY OF THE INVENTION

Improved porous particles for drug delivery to the pulmonary system, and methods for their synthesis and administration are provided. In a preferred embodiment, the porous particles are made of a biodegradable material and have a mass density less than 0.4 g/cm.sup.3. The particles may be formed of biodegradable materials such as biodegradable polymers. For example, the particles may be formed of a functionalized polyester graft copolymer consisting of a linear .alpha.-hydroxy-acid polyester backbone having at least one amino acid group incorporated therein and at least one poly(amino acid) side chain extending from an amino acid group in the polyester backbone. In one embodiment, porous particles having a relatively large mean diameter, for example, greater than 5 .mu.m, can be used for enhanced delivery of a therapeutic agent to the airways or the alveolar region of the lung. The porous particles incorporating a therapeutic agent may be effectively aerosolized for administration to the respiratory tract to permit systemic or local delivery of a wide variety of therapeutic agents.

DETAILED DESCRIPTION OF THE INVENTION

Biodegradable particles for improved delivery of therapeutic agents to the respiratory tract are provided. The particles can be used in one embodiment for controlled systemic or local drug delivery to the respiratory tract via aerosolization. In one embodiment, the particles are porous particles having a mass density less than 1.0 g/cm.sup.3, preferably less than about 0.4 g/cm.sup.3. The porous structure permits deep lung delivery of relatively large diameter therapeutic aerosols, for example greater than 5 .mu.m in mean diameter. The particles also may include a rough surface texture which can reduce particle agglomeration and provide a highly flowable powder, which is ideal for aerosolization via dry powder inhaler devices, leading to lower deposition in the mouth and throat.

Mass Density and Diameter of Porous Particles

As used herein the term "porous particles" refers to particles having a total mass density less than about 0.4 g/cm.sup.3. The mean diameter of the particles can range, for example, from about 100 nm to 15 .mu.m, or larger depending on factors such as particle composition, and the targeted site of the respiratory tract for deposition of the particle.

Particle Size

In one embodiment, particles which are macroscopically porous, and incorporate a therapeutic drug, and having a mass density less than about 0.4 g/cm.sup.3, can be made with mean diameters greater than 5 .mu.m, such that they are capable of escaping inertial and gravitational deposition in the oropharyngeal region, and are targeted to the airways or the deep lung. The use of larger porous particles is advantageous since they are able to aerosolize more efficiently than smaller, non-porous aerosols such as those currently used for inhalation therapies.

The large (>5 .mu.m) porous particles are also advantageous in that they can more successfully avoid phagocytic engulfment by alveolar macrophages and clearance from the lungs, in comparison to smaller non-porous particles, due to size exclusion of the particles from the phagocytes' cytosolic space. Phagocytosis of particles by alveolar macrophages diminishes precipitously as particle diameter increases beyond 3 .mu.m. Kawaguchi, H. et al., Biomaterials, 7:61-66 (1986); Krenis, L. J. and Strauss, B., Proc. Soc. Exp. Med., 107:748-750 (1961); and Rudt, S. and Muller, R. H., J. Contr. Rel., 22:263-272 (1992). The porous particles thus are capable of a longer term release of a therapeutic agent. Following inhalation, porous degradable particles can deposit in the lungs (due to their relatively low mass density), and subsequently undergo slow degradation and drug release, without the majority of the particles being phagocytosed by alveolar macrophages. The drug can be delivered relatively slowly into the alveolar fluid, and at a controlled rate into the blood stream, minimizing possible toxic responses of exposed cells to an excessively high concentration of the drug. The porous polymeric particles thus are highly suitable for inhalation therapies, particularly in controlled release applications. The preferred diameter for porous particles for inhalation therapy is greater than 5 .mu.m, for example between about 5-15 .mu.m.

The particles also may be fashioned with the appropriate material, diameter and mass density for localized delivery to other regions of the respiratory tract such as the upper airways. For example higher density or larger particles may be used for upper airway delivery.

Particle Deposition

Inertial impaction and gravitational settling of aerosols are predominant deposition mechanisms in the airways and acini of the lungs during normal breathing conditions. Edwards, D. A., J. Aerosol Sci., 26:293-317 (1995). Both deposition mechanisms increase in proportion to the mass of aerosols and not to particle volume. Since the site of aerosol deposition in the lungs is determined by the intrinsic mass of the aerosol (at least for particles of mean aerodynamic diameter greater than approximately 1 .mu.m), diminishing particle mass density by increasing particle porosity permits the delivery of larger particles into the lungs, all other physical parameters being equal.

The low mass porous particles have a small aerodynamic diameter in comparison to the actual sphere diameter. The aerodynamic diameter, d.sub.ae, is related to the actual sphere diameter, d (Gonda, I., "Physico-chemical principles in aerosol delivery," In Topics in Pharmaceutical Sciences, 1991, (eds. D. J. A. Crommelin and K. K. Midha), pp. 95-117, Stuttgart: Medpharm Scientific Publishers, 1992) by the formula: d.sub.aer=d.sub. .rho. where the particle mass density .rho. is in units of g/cm.sup.3. Maximal deposition of monodisperse aerosol particles in the alveolar region of the human lung (.about.60%) occurs for an aerodynamic diameter of approximately d.sub.aer=3 .mu.m. Heyder, J. et al., J. Aerosol Sci., 17: 811-825 (1986). Due to their small mass density, the actual diameter d of porous particles comprising a mondisperse inhaled powder that will exhibit maximum deep-lung deposition is: d=3/ .rho..mu.m (where .rho.<1); where d is always greater than 3 .mu.m. For example, porous particles that display a mass density, .rho.=0.1 g/cm.sup.3, will exhibit a maximum deposition for particles having actual diameters as large as 9.5 .mu.m. The increased particle size diminishes interparticle adhesion forces. Visser, J., Powder Technology, 58:1-10. Thus, large particle size increases efficiency of aerosolization to the deep lung for particles of low mass density. Particle Materials

The porous particles preferably arc biodegradable and biocompatible, and optionally are capable of biodegrading at a controlled rate for delivery of a drug. The porous particles can be made of any material which is capable of forming a porous particle having a mass density less than about 0.4 g/cm.sup.3. Both inorganic and organic materials can be used. For example, ceramics may be used. Other non-polymeric materials may be used which are capable of forming porous particles as defined herein.

Polymeric Particles

The particles may be formed from any biocompatible, and preferably biodegradable polymer, copolymer, or blend, which is capable of forming porous particles having a density less than about 0.4 g/cm.sup.3.

Surface eroding polymers such as polyanhydrides may be used to form the porous particles. For example, polyanhydrides such as poly[(p-carboxyphenoxy)hexane anhydride] ("PCPH") may be used. Biodegradable polyanhydrides are described, for example, in U.S. Pat. No. 4,857,311, the disclosure of which is incorporated herein by reference.

In another embodiment, bulk eroding polymers such as those based on polyesters including poly(hydroxy acids) can be used. For example, polyglycolic acid ("PGA") or polylactic acid ("PLA") or copolymers thereof may be used to form the porous particles, wherein the polyester has incorporated therein a charged or functionalizable group such as an amino acid as described below.

Other polymers include polyamides, polycarbonates, polyalkylenes such as polyethylene, polypropylene, poly(ethylene glycol), poly(ethylene oxide), poly(ethylene terephthalate), polyvinyl compounds such as polyvinyl alcohols, polyvinyl ethers, and polyvinyl esters, polymers of acrylic and methacrylic acids, celluloses, polysaccharides, and peptides or proteins, or copolymers or blends thereof which are capable of forming porous particles with a mass density less than about 0.4 g/cm.sup.3. Polymers may be selected with or modified to have the appropriate stability and degradation rates in vivo for different controlled drug delivery applications.

Polyester Graft Copolymers

In one preferred embodiment, the porous particles are formed from functionalized polyester graft copolymers, as described in Hrkach et al., Macromolecules, 28:4736-4739 (1995); and Hrkach et al., "Poly(L-Lactic acid-co-amino acid) Graft Copolymers: A Class of Functional Biodegradable Biomaterials" In Hydrogel and Biodegradable Polymers for Bioapplications, ACS Symposium Series No. 627, Raphael M. Ottenbrite et al., Eds., American Chemical Society, Chapter 8, pp. 93-101, 1996, the disclosures of which are incorporated herein by reference. The functionalized graft copolymers are copolymers of polyesters, such as poly(glycolic acid) or poly(lactic acid), and another polymer including functionalizable or ionizable groups, such as a poly(amino acid). In a preferred embodiment, comb-like graft copolymers are used which include a linear polyester backbone having amino acids incorporated therein, and poly(amino acid) side chains which extend from the amino acid groups in the polyester backbone. The polyesters may be polymers of .alpha.-hydroxy acids such as lactic acid, glycolic acid, hydroxybutyric acid and valeric acid, or derivatives or combinations thereof. The inclusion of ionizable side chains, such as polylysine, in the polymer has been found to enable the formation of more highly porous particles, using techniques for making microparticles known in the art, such as solvent evaporation. Other ionizable groups, such as amino or carboxyl groups, may be incorporated, covalently or noncovalently, into the polymer to enhance porosity. For example, polyaniline could be incorporated into the polymer.

An exemplary polyester graft copolymer, which may be used to form porous polymeric particles is the graft copolymer, poly(lactic acid-co-lysine-graft-lysine) ("PLAL-Lys"), which has a polyester backbone consisting of poly(L-lactic acid-co-Z-L-lysine) (PLAL), and grafted lysine chains. PLAL-Lys is a comb-like graft copolymer having a backbone composition, for example, of 98 mol % lactic acid and 2 mol % lysine and poly(lysine) side chains extending from the lysine sites of the backbone.

PLAL-Lys may be synthesized as follows. First, the PLAL copolymer consisting of L-lactic acid units and approximately 1-2% N.epsilon.-carbobenzoxy-L-lysine (Z-L-lysine) units is synthesized as described in Barrera et al., J. Am. Chem. Soc., 115:11010 (1993). Removal of the Z protecting groups of the randomly incorporated lysine groups in the polymer chain of PLAL yields the free e-amine which can undergo further chemical modification. The use of the poly(lactic acid) copolymer is advantageous since it biodegrades into lactic acid and lysine, which can be processed by the body. The existing backbone lysine groups are used as initiating sites for the growth of poly(amino acid) side chains.

The lysine .epsilon.-amine groups of linear poly(L-lactic acid-co-L-lysine) copolymers initiate the ring opening polymerization of an amino acid N-carboxyanhydride (NCA) to produce poly(L-lactic acid-co-amino acid) comb-like graft copolymers. In a preferred embodiment, NCAs are synthesized by reacting the appropriate amino acid with triphosgene. Daly et al., Tetrahedron Lett., 29:5859 (1988). The advantage of using triphosgene over phosgene gas is that it is a solid material, and therefore, safer and easier to handle. It also is soluble in THF and hexane so any excess is efficiently separated from the NCAs.

The ring opening polymerization of amino acid N-carboxyanhydrides (NCAs) is initiated by nucleophilic initiators such as amines, alcohols, and water. The primary amino initiated ring opening polymerization of NCAs allows good control over the degree of polymerization when the monomer to initiator ratio (M/I) is less than 150. Kricheldorf, H. R. In Models of Biopolymers by Ring-Opening Polymerization, Penezek, S., Ed., CRC Press, Boca Raton, 1990, Chapter 1; Kricheldorf, H. R., .alpha.-Aminoacid-N-Carboxy-Anhydrides and Related Heterocycles, Springer-Verlag, Berlin, 1987; and Imanishi, Y. In Ring-Opening Polymerization, Ivin, K. J. and Saegusa, T., Eds., Elsevier, London, 1984, Volume 2, Chapter 8. Methods for using lysine .epsilon.-amine groups as polymeric initiators for NCA polymerizations are described in the art. Sela, M. et al., J. Am. Chem. Soc., 78:746 (1956).

In the reaction of an amino acid NCA with PLAL, the nucleophilic primary .epsilon.-amine of the lysine side chain attacks C-5 of the NCA leading to ring opening and formation of the amino acid amide along with the evolution of CO.sub.2. Propagation takes place via further attack of the amine group of the amino acid amides on subsequent NCA molecules. The degree of polymerization of the poly(amino acid) side chains, the corresponding amino acid content in the graft copolymers and their resulting physical and chemical characteristics can be controlled by changing the M/I ratio for the NCA polymerization--that is, changing the ratio of NCA to lysine .epsilon.-amine groups of pLAL. Thus, in the synthesis, the length of the poly(amino acid), such as poly(lysine), side chains and the total amino acid content in the polymer may be designed and synthesized for a particular application.

The poly(amino acid) side chains grafted onto or incorporated into the polyester backbone can include any amino acid, such as aspartic acid, alanine or lysine, or mixtures thereof. The functional groups present in the amino acid side chains, which can be chemically modified, include amino, carboxylic acid, sulfide, guanidino, imidazole and hydroxyl groups. As used herein, the term "amino acid" includes natural and synthetic amino acids and derivatives thereof. The polymers can be prepared with a range of amino acid side chain lengths, for example, about 10-100 or more amino acids, and with an overall amino acid content of, for example, 7-72% or more depending on the reaction conditions. The grafting of poly(amino acids) from the pLAL backbone may be conducted in a solvent such as dioxane, DMF, or CH.sub.2Cl.sub.2 or mixtures thereof. In a preferred embodiment, the reaction is conducted at room temperature for about 2-4 days in dioxane.

Alternatively, the porous particles for pulmonary drug delivery may be formed from polymers or blends of polymers with different polyester/amino acid backbones and grafted amino acid side chains. For example, poly(lactic acid-co-lysine-graft-alanine-lysine) ("PLAL-Ala-Lys"), or a blend of PLAL-Lys with poly(lactic acid-co-glycolic acid-block-ethylene oxide) ("PLGA-PEG") ("PLAL-Lys-PLGA-PEG") may be used.

In the synthesis, the graft copolymers may be tailored to optimize different characteristic of the porous particle including: i) interactions between the agent to be delivered and the copolymer to provide stabilization of the agent and retention of activity upon delivery; ii) rate of polymer degradation and, thereby, rate of drug release profiles; iii) surface characteristics and targeting capabilities via chemical modification; and iv) particle porosity.

Formation of Porous Polymeric Particles

Porous polymeric particles may be prepared using single and double emulsion solvent evaporation, spray drying, solvent extraction and other methods well known to those of ordinary skill in the art. Methods developed for making microspheres for drug delivery are described in the literature, for example, as described by Mathiowitz and Langer, J. Controlled Release, 5:13-22 (1987); Mathiowitz, et al., Reactive Polymers, 6:275-283 (1987); and Mathiowitz, et al., J. Appl. Polymer Sci. 35:755-774 (1988), the teachings of which are incorporated herein. The selection of the method depends on the polymer selection, the size, external morphology, and crystallinity that is desired, as described, for example, by Mathiowitz, et al., Scanning Microscopy, 4:329-340 (1990); Mathiowitz, et al., J. Appl. Polymer Sci., 45:125-134 (1992); and Benita, et al., J. Pharm. Sci., 73:1721-1724 (1984), the teachings of which are incorporated herein.

In solvent evaporation, described for example, in Mathiowitz, et al., (1990), Benita, and U.S. Pat. No. 4,272,398 to Jaffe, the polymer is dissolved in a volatile organic solvent, such as methylene chloride. Several different polymer concentrations can be used, for example, between 0.05 and 0.20 g/ml. The drug, either in soluble form or dispersed as fine particles, is added to the polymer solution, and the mixture is suspended in an aqueous phase that contains a surface active agent such as poly(vinyl alcohol). The aqueous phase may be, for example, a concentration of 1% poly (vinyl alcohol) w/v in distilled water. The resulting emulsion is stirred until most of the organic solvent evaporates, leaving solid microspheres, which may be washed with water and dried overnight in a lyophilizer.

Microspheres with different sizes (1-1000 microns) and morphologies can obtained by this method which is useful for relatively stable polymers such as polyesters and polystryrene. However, labile polymers such as polyanhydrides may degrade due to exposure to water. For these polymers, solvent removal may be preferred.

Solvent removal was primarily designed for use with polyanhydrides. In this method, the drug is dispersed or dissolved in a solution of a selected polymer in a volatile organic solvent like methylene chloride. The mixture is then suspended in oil, such as silicon oil, by stirring, to form an emulsion. Within 24 hours, the solvent diffuses into the oil phase and the emulsion droplets harden into solid polymer microspheres. Unlike solvent evaporation, this method can be used to make microspheres from polymers with high melting points and a wide range of molecular weights. Microspheres having a diameter for example between one and 300 microns can be obtained with this procedure.

Targeting of Particles

Targeting molecules can be attached to the porous particles via reactive functional groups on the particles. For example, targeting molecules can be attached to the amino acid groups of functionalized polyester graft copolymer particles, such as PLAL-Lys particles. Targeting molecules permit binding interaction of the particle with specific receptor sites, such as those within the lungs. The particles can be targeted by attachment of ligands which specifically or non-specifically bind to particular targets. Exemplary targeting molecules include antibodies and fragments thereof including the variable regions, lectins, and hormones or other organic molecules capable of specific binding for example to receptors on the surfaces of the target cells.

Therapeutic Agents

Any of a variety of therapeutic, prophylactic or diagnostic agents can be delivered. Examples include synthetic inorganic and organic compounds, proteins and peptides, polysaccharides and other sugars, lipids, and nucleic acid sequences having therapeutic, prophylactic or diagnostic activities. Nucleic acid sequences include genes, antisense molecules which bind to complementary DNA to inhibit transcription, and ribozymes. The agents to be incorporated can have a variety of biological activities, such as vasoactive agents, neuroactive agents, hormones, anticoaguulants, immunomodulating agents, cytotoxic agents, antibiotics, antivirals, antisense, antigens, and antibodies. In some instances, the proteins may be antibodies or antigens which otherwise would have to be administered by injection to elicit an appropriate response. Compounds with a wide range of molecular weight can be encapsulated, for example, between 100 and 500,000 grams per mole.

Proteins are defined as consisting of 100 amino acid residues or more; peptides are less than 100 amino acid residues. Unless otherwise stated, the term protein refers to both proteins and peptides. Examples include insulin and other hormones. Polysaccharides, such as heparin, can also be administered.

The porous polymeric aerosols are useful as carriers for a variety of inhalation therapies. They can be used to encapsulate small and large drugs, release encapsulated drugs over time periods ranging from hours to months, and withstand extreme conditions during aerosolization or following deposition in the lungs that might otherwise harm the encapsulated therapeutic.

The porous particles may include a therapeutic agent for local delivery within the lung, such as agents for the treatment of asthma, emphysema, or cystic fibrosis, or for systemic treatment. For example, genes for the treatment of diseases such as cystic fibrosis can be administered.

Administration

The particles including a therapeutic agent may be administered alone or in any appropriate pharmaceutical carrier, such as a liquid, for example saline, or a powder, for administration to the respiratory system.

Aerosol dosage, formulations and delivery systems may be selected for a particular therapeutic application, as described, for example in Gonda, I. "Aerosols for delivery of therapeutic and diagnostic agents to the respiratory tract," In Critical Reviews in Therapeutic Drug Carrier Systems, 6:273-313 (1990), and in Moren, "Aerosol dosage forms and formulations," In Aerosols in Medicine. Principles, Diagnosis and Therapy, Moren, et al., Eds., Esevier, Amsterdam, 1985, the disclosures of which are incorporated herein by reference.

The greater efficiency of aerosolization by porous particles of relatively large size permits more drug to be delivered than is possible with the same mass of nonporous aerosols. The relative large size of porous aerosols depositing in the deep lungs also minimizes potential drug losses caused by particle phagocytosis. The use of porous polymeric aerosols as therapeutic carriers provides the benefits of biodegradable polymers for controlled released in the lungs and long-time local action or systemic bioavailability. Denaturation of macromolecular drugs can be minimized during aerosolization since macromolecules are contained and protected within a polymeric shell. Coencapsulation of peptides with peptidase-inhibitors can minimize peptide enzymatic degradation.
 

Claim 1 of 22 Claims

1. Therapeutic particles suitable for aerosolization in a dry powder inhaler (DPI) comprising, a therapeutic agent and a pharmaceutically acceptable carrier, wherein the particles are porous, have a tap density less than about 0.4 g/cm.sup.3 and wherein upon aerosolization, about 80% of the particles exit the DPI and at least 55% of the particles exiting the DPI have an aerodynamic diameter of less than about 4.7 .mu.m as measured by a cascade impactor for 30 seconds at 28.3 l/min flow rate.

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