Title:  Temperature sensitive gel for sustained delivery of protein drugs

United States Patent:  6,482,435

Issued:  November 19, 2002

Inventors:  Stratton; Lewis P. (Greenville, SC); Carpenter; John F. (Littleton, CO); Manning; Mark C. (Fort Collins, CO)

Assignee:  University Technology Corporation (Boulder, CO)

Appl. No.:  232288

Filed:  January 15, 1999

Pharmaceutical compositions for the delivery of pharmacologically active proteins are provided by the present invention. The compositions of the present invention comprise a polymeric matrix having thermal gelation properties in which is incorporated a discrete suspension of at least one biologically active macromolecular polypeptide which retains greater than 90 percent of its biological activity. Furthermore, the concentration of the macromolecular polypeptide is greater than 0.5 percent by weight of the composition.

DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENT

The pharmaceutical device or composition of the present invention provides a delivery system for the controlled and sustained administration of fully native macromolecular polypeptides or therapeutic agents to a human or animal. The biodegradable, biocompatible matrix for drug delivery is formed by suspending soluble and insoluble particles of fully native macromolecular polypeptides having a concentration of 5 mg/ml or greater, and other protein stabilizing components uniformly and discretely throughout a pharmaceutical vehicle or polymer matrix that exhibits reverse thermal gelation characteristics. As with previously known systems, the suspended particles and other components are released through a combination of diffusion and dissolution mechanisms as the device hydrates and subsequently erodes or dissolves. However, unlike known polymeric matrix systems which deliver macromolecules, the composition of this invention comprises a suspension as opposed to a solution of native polypeptide(s). Consequently, high polypeptide concentrations are attained as a result of the suspension, thus achieving the ability for sustained administration of the therapeutic agent for a time period of days, weeks or months as opposed to hours. Furthermore, stabilizing agents may be incorporated into the composition of the present invention thereby further minimizing the degradation of these drugs, which directly impacts the efficacy of the drug and the ability to store or ship the device to worldwide markets.

The pharmaceutical composition of the present invention is a serendipitous discovery that was made during a research project, the goal of which was simply to identify a drug delivery system that was amenable to study the effect of polymeric matrices on protein structure. In that study, Fourier transform infrared spectroscopy was employed, because it can be used to analyze protein secondary structure in solutions, suspensions, and solids. Of the various protein drug delivery matrices disclosed in the literature, those employing the polymeric detergent, Pluronic.RTM. F-127, which forms a temperature sensitive gel, were the most attractive for infrared spectroscopic studies, as it did not appear (based on the structures of poloxamer) that poloxamers would have an infrared absorbance that would interfere with the protein absorbance signal, which is needed for structural evaluation. Furthermore, it had previously been established that poloxamers, at sufficient concentrations, have the characteristics of being liquid at temperatures below room temperature but will form into gel as they are warmed. Thus, a further objective of the study was to determine what effect this liquid to gel transition of the poloxamer would have on the protein's structure. In order to study protein structure with infrared spectroscopy it is necessary to have protein concentrations of at least 15-20 mg/ml, thus a protein concentration of 20 mg/ml was prepared in the presence of sufficient poloxamer to allow gelling during warming. The resulting protein solution formed a fine, milky suspension, which was initially very disappointing, because the formation of such suspensions often indicates that a solution component (e.g., the polymeric detergent) caused the protein to denature and to form non-native or inactive protein aggregates, thus indicating failure of the test. However, infrared spectroscopy can, fortunately, be used to analyze protein structures in suspension, so the suspension was analyzed anyway. Surprisingly, when the protein suspension was analyzed with the Fourier transform infrared spectroscopy, instead of finding the expected non-native or inactive protein aggregates, it was unexpectedly found to be fully native.

In accordance with the present invention, the pharmaceutical composition of the present invention comprises a polymer such as a polyoxyalkylene block copolymer of formula:

HO (C₂ H₄ O)_b (C₃ H₆ O)_a (C₂ H₄ O)_b H (I)

which has the unique feature, in the preferred embodiment, of being liquid at ambient or lower temperatures and existing as a semi-solid gel at mammalian body temperatures wherein a and b are integers in the range of 20 to 80 and 15 to 60, respectively. A preferred polyoxyalkylene block copolymer for use as the pharmaceutical vehicle of this invention is a polyoxyethylene-polyoxypropylene block copolymer having the following formula:

HO--(CH₂ CH₂ O)_b --(CH₂ (CH₃)CHO)_a --(CH₂ CH₂ O)_b --H (II)

wherein a and b are integers such that the hydrophobe base represented by (CH₂ (CH₃)CHO)_a has a molecular weight of at least about 4,000, as determined by hydroxyl number; the polyoxyethylene chain constituting about 70 percent of the total number of monomeric units in the molecule and where the copolymer has an average molecular weight of about 12,600. Pluronic.RTM. F-127, also known as Poloxamer 407, is such a material.

The procedures used to prepare aqueous solutions which form gels of polyoxyalkylene block copolymer are well known. For example, either a hot or cold process for forming the solutions can be used. The cold technique involves the steps of dissolving the polyoxalkylene block copolymer at a temperature of about 5^oC. to 10^oC. in water or in a buffer, such as a phosphate buffer. The water, if used in forming the aqueous solution, is preferably purified, as by distillation, filtration, ion-exchange or the like. When the solution is complete it is brought to room temperature whereupon it forms a gel. If the hot process of forming the gel is used, the polymer is added to water or a buffer and heated to a temperature of about 75^oC. to 85^oC. with slow stirring until a clear homogenous solution is obtained, upon cooling a clear gel forms.

Any macromolecular polypeptide may be mixed with the pharmaceutical vehicle to form the pharmaceutical composition of this invention wherein the concentration of macromolecular polypeptide is in the range of 0.5 to 50 percent by weight of the composition. 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.

Exemplary classes of polypeptides include, among others, proteins, enzymes, nucleoproteins, glycoproteins, lipoproteins, hormonally active polypeptides, and synthetic analogues including agonists and antagonists of these molecules.

Specific examples of polypeptides suitable for incorporation in the delivery system of the present invention include the following biologically active macromolecules: interferons, interleukins, insulin, enzyme inhibitors, colony-stimulating factors, plasminogen activators, growth factors and polypeptide hormones.

The list of macromolecular polypeptides recited above are provided only to illustrate the types of active agents which are suitable for use in practicing the present invention, and are not intended to limit the scope of the present invention.

The pharmaceutical composition of the present invention can be readily prepared using any solution forming technique which achieves the concentration of polyoxyalkylene block copolymer necessary for gelling. Preferably the pharmaceutical vehicle and polypeptide mixture are prepared separately and the polypeptide mixture having a concentration of 5 mg/ml or greater is added thereto at a temperature of about 0^oC. to 10^oC. When combined the protein forms a homogenous suspension of fine particles in the polymer solution, which then has a "milky" appearance. By light microscopy the particles are approximately 5-10 microns in diameter. Raising the sample temperature above the gel point of the poloxamer results in an even distribution of protein particles throughout the polymer gel. Due to the high viscosity of the gel matrix, the particles remain homogeneously distributed and do not "settle out." The liquid to gel transition is fully reversible upon cooling. Furthermore, when the gel is exposed to an aqueous solution, the gel matrix and protein particles dissolve, releasing the fully native protein which retains greater than 90 percent of its biological activity.

The pharmaceutical composition of the present invention can be implanted directly into the body by injecting it as a liquid, whereupon the pharmaceutical composition will gel once inside the body. In the alternative, the pharmaceutical composition may be introduced into a small implantable pump which is then introduced into the body.

In another embodiment, protein-stabilizing solutes, can be incorporated into the pharmaceutical device of the present invention described above. Initially, stabilizers were added to the pharmaceutical device of the present invention to increase the stability of the macromolecular polypeptides as such stabilization would be crucial for use of the present invention for sustained delivery of protein in the body. However, in doing so it was discovered that protein-stabilizing solutes, such as sucrose not only aid in protecting and stabilizing the protein, but also allow the poloxamer to form suitable gels at lower concentrations than needed in water or buffer alone. Thus, the working range of polymer concentration can be widened. As discussed previously, the concentration of the polyoxyalkylene block copolymer is an important parameter. It is known that a gel will not form when the concentration of polyoxyalkylene-polyoxypropylene block copolymer in water or dilute buffer is outside of the range of about 20 to 30 percent by weight, as shown in FIG. 1 and exemplified by the line having open triangles. However, by introducing protein-stabilizing solutes to the pharmaceutical device of the present invention the gel-sol transition temperature may be manipulated, while also lowering the concentration of polyoxyethelene-polyoxypropylene block copolymer which is necessary to form a gel.

In a third embodiment, polypeptide concentrations at the high end of the 0.5 to 50 percent by weight range can be achieved by centrifuging the pharmaceutical composition of the present invention at low temperatures in the range of -10^oC. to 10^oC., and preferably 0-4^o C. for a period of time sufficient to sediment the protein particles. For example, a sample of the pharmaceutical composition described previously comprising 20 mg/ml protein can be centrifuged at 4^oC. so that the insoluble protein particles sediment. Then supernatant equivalent to half the volume could be removed and the sediment resuspended in the remaining liquid. This will result in a suspension containing almost 40 mg/ml.

In the Examples which follow the pharmaceutical composition of the present invention was prepared according to the following preparation procedure. Since the polyoxyalkylenes dissolve more completely at reduced temperatures, the preferred methods of solubilization are to add the required amount of copolymer to the amount of water or buffer to be used. Generally after wetting the copolymer by shaking, the mixture is capped and placed in a cold chamber or in a thermostatic container at about 0^oC. to 10^oC. in order to dissolve the copolymer. The mixture can be stirred or shaken to bring about a more rapid solution of the polymer. The polypeptides and various additives such as stabilizers can subsequently-be added and dissolved to form a suspension.

The following non-limited examples provide methods for preparing temperature sensitive polymers for the sustained delivery of pharmaceutical agents comprising high concentrations of fully native macromolecular polypeptide agents. All scientific and technical terms have the meanings as understood by one with ordinary skill in the art. The specific examples which follow, illustrate the representative polypeptides and concentrations capable of being achieved by the present invention and are not to be construed as limiting the invention in sphere or scope. The methods may be adapted to variation in order to produce compositions or devices embraced by this invention but not specifically disclosed. Further variations of the methods to produce the same compositions in somewhat different fashion will be evident to one skilled in the art.

All temperatures are understood to be in Centigrade (^oC.) when not specified. The infrared (IR) spectral description was measured on a Nicolet Magna-IR 550 Spectrometer. Commercially available chemicals were used without purification.

Claim 1 of 10 Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of varying the liquid-gel transition temperature of a polyoxyalkylene block copolymer having the formula: HO(C₂ H₄ O)_b (C₃ H₆ O)_a (C₂ H₄ O)_b H, wherein a is 20 to 80 and b is 15 to 60, the method comprising adding a solute selected from the group consisting of a sugar and a polyether glycol to an aqueous solution of said copolymer so as to increase or decrease said transition temperature.
 

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