Emulsion vehicle for poorly soluble drugs

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EMULSION VEHICLE FOR POORLY
SOLUBLE DRUGS

RELATED APPLICATIONS

This application is a non-provisional application based on U.S. Provisional Application No. 60/034,188 filed Jan. 7, 1997 and U.S. Provisional Application No. 60/048,840 filed Jun. 6,1997 and claims the benefit of these filing dates under 35 U.S.C. § 119(e) for priority purposes.

BACKGROUND OF THE INVENTION

Hundreds of medically useful compounds are discovered each year, but clinical use of these drugs is possible only if a drug delivery vehicle is developed to transport them to 15 their therapeutic target in the human body. This problem is particularly critical for drugs requiring intravenous injection in order to reach their therapeutic target or dosage but which are water insoluble or poorly water soluble. For such hydrophobic compounds, direct injection may be impossible or 20 highly dangerous, and can result in hemolysis, phlebitis, hypersensitivity, organ failure and/or death. Such compounds are termed by pharmacists "lipophilic", "hydrophobic", or in their most difficult form, "amphiphobic". 25

A few examples of therapeutic substances in these categories are ibuprofen, diazepam, griseofulvin, cyclosporin, cortisone, proleukin, etoposide and paclitaxel. Kagkadis, K A et al. (1996) PDA J Pharm Sci Tech 50(5):317-323; Dardel, O. 1976. Anaesth Scand 20:221-24. Sweetana, S 30 and M J U Akers. (1996) PDA J Pharm Sci Tech 50(5) :330-342.

Administration of chemotherapeutic or anti-cancer agents is particularly problematic. Low solubility anti-cancer 3J agents are difficult to solubilize and supply at therapeutically useful levels. On the other hand, water-soluble anti-cancer agents are generally taken up by both cancer and non-cancer cells thereby exhibiting non-specificity.

Efforts to improve water-solubility and comfort of admin- 40 istration of such agents have not solved, and may have worsened, the two fundamental problems of cancer chemotherapy: 1) non-specific toxicity and 2) rapid clearance form the bloodstream by non-specific mechanisms. In the case of cytotoxins, which form the majority of currently available 45 chemotherapies, these two problems are clearly related. Whenever the therapeutic is taken up by noncancerous cells, a diminished amount of the drug remains available to treat the cancer, and more importantly, the normal cell ingesting the drug is killed. 50

To be effective in treating cancer, the chemotherapeutic must be present throughout the affected tissue(s) at high concentration for a sustained period of time so that it may be taken up by the cancer cells, but not at so high a concentration that normal cells are injured beyond repair. 55 Obviously, water soluble molecules can be administered in this way, but only by slow, continuous infusion and monitoring, aspects which entail great difficulty, expense and inconvenience.

A more effective method of administering a cancer 60 therapeutic, particularly a cytotoxin, is in the form of a dispersion of oil in which the drug is dissolved. These oily particles are made electrically neutral and coated in such a way that they do not interact with plasma proteins and are not trapped by the reticuloendothelial system (RES), instead 65 remaining intact in the tissue or blood for hours, days or even weeks. In most cases, it is desirable if the particles also

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distribute themselves into the surrounding lymph nodes which are injected at the site of a cancer. Nakamoto, Y et al. (1975) Chem Pharm Bull 23(10):2232-2238. Takahashi, T et al. (1977) Tohoku J Exp Med 123:235-246. In many cases direct injection into blood is the route of choice for administration. Even more preferable, following intravenous injection, the blood-borne particles may be preferentially captured and ingested by the cancer cells themselves. An added advantage of a particulate emulsion for the delivery of a chemotherapeutic is the widespread property of surfactants used in emulsions to overcome multidrug resistance.

For drugs that cannot be formulated as an aqueous solution, emulsions have typically been most cost-effective and gentle to administer, although there have been serious problems with making them sterile and endotoxin free so that they may be administered by intravenous injection. The oils typically used for pharmaceutical emulsions include saponifiable oils from the family of triglycerides, for example, soybean oil, sesame seed oil, cottonseed oil, safflower oil and the like. Hansrani, P K et al., (1983) J Parenter Sci Technol 37:145-150. One or more surfactants are used to stabilize the emulsion, and excipients are added to render the emulsion more biocompatible, stable and less toxic. Lecithin from egg yolks or soybeans is a commonly used surfactant. Sterile manufacturing can be accomplished by absolute sterilization of all the components before manufacture, followed by absolutely aseptic technique in all stages of manufacture. However, improved ease of manufacture and assurance of sterility is obtained by terminal sterilization following sanitary manufacture, either by heat or by filtration. Unfortunately, not all emulsions are suitable for heat or filtration treatments.

Stability has been shown to be influenced by the size and homogeneity of the emulsion. The preferred emulsion consists of a suspension of sub-micron particles, with a mean size of no greater than 200 nanometers. A stable dispersion in this size range is not easily achieved, but has the benefit that it is expected to circulate longer in the bloodstream. Further, less of the stable dispersion is phagocytized nonspecifically by the reticuloendothelial system. As a result the drug is more likely to reach its therapeutic target. Thus, a preferred drug emulsion will be designed to be actively taken up by the target cell or organ, and is targeted away from the RES.

The use of vitamin E in emulsions is known. In addition to the hundreds of examples where vitamin E in small quantities [for example, less than 1%, R T Lyons. Pharm Res 13(9): S-226, (1996) "Formulation development of an injectable oil-in-water emulsion containing the lipophilic antioxidants K-tocopherol and P-carotene"] is used as an anti-oxidant in emulsions, the first primitive, injectable vitamin E emulsions per se were made by Hidiroglou for dietary supplementation in sheep and for research on the pharmacokinetics of vitamin E and its derivatives. Hidiroglou M and Karpinski K. (1988) Brit J Nutrit 59:509-518.

For mice, an injectable form of vitamin E was prepared by Kato and coworkers. Kato Y, et al. (1993) Chem Pharm Bull 41(3):599-604. Micellar solutions were formulated with Tween 80, Brij 58 and HCO-60. Isopropanol was used as a co-solvent, and was then removed by vacuum evaporation; the residual oil glass was then taken up in water with vortexing as a micellar suspension. An emulsion was also prepared by dissolving vitamin E with soy phosphatidycholine (lecithin) and soybean oil. Water was added and the emulsion prepared with sonication.

In 1983, E-Ferol, a vitamin E emulsion was introduced for vitamin E supplementation and therapy in neonates. Alade S 3 a vitamin E derivative comprising a peptide bonded polyglutamate attached to the ring hydroxyl and pegylated phytosterol.

L et al. (1986) Pediatrics 77(4):593-597. Within a few months over 30 babies had died as a result of receiving the product, and the product was promptly withdrawn by FDA order. The surfactant mixture used in E-Ferol to emulsify 25 mg/mL vitamin E consisted of 9% Tween 80 and 1% Tween 5 20. These surfactants seem ultimately to have been responsible for the unfortunate deaths. This experience illustrates the need for improved formulations and the importance of selecting suitable biocompatible surfactants and carefully monitoring their levels in parenteral emulsions and. 10

An alternative means of solubilizing low solubility compounds is direct solubilization in a non-aqueous milieu, for example alcohol (such as ethanol) dimethylsulfoxide or triacetin. An example in PCT application WO 95/11039 describes the use of vitamin E and the vitamin E derivative 15 TPGS in combination with ethanol and the immunosuppressant molecule cyclosporin. Alcohol-containing solutions can be administered with care, but are typically given by intravenous drip to avoid the pain, vascular irritation and toxicity associated with bolus injection of these solutions. 20

Problems with pharmaceutical formulations in nonaqueous solvents and solubilizers such as alcohol (ethanol, isopropanol, benzyl alcohol, etc.) relate to the ability of these solvents to extract toxic substances, for example plasticizers, from their containers. The current commercial 25 formulation for the anti-cancer drug paclitaxel, for example, consists of a mixture of hydroxylated castor oil and ethanol, and rapidly extracts plasticizers such as di-(2-ethylhexyl)phthalate from commonly used intravenous infusion tubing and bags. Adverse reactions to the plasticizers have been 30 reported, such as respiratory distress, necessitating the use of special infusion systems at extra expense and time. Waugh, et al. (1991) Am J Hosp Pharmacists 48:1520.

In light of these problems, it can be seen that the ideal emulsion vehicle would be inexpensive, non-irritating or even nutritive and palliative in itself, terminally sterilizable by either heat or filtration, stable for at least 1 year under controlled storage conditions, accommodate a wide variety of water insoluble and poorly soluble drugs and be substantially ethanol-free. In addition to those drugs which are lipophilic and dissolve in oils, also needed is a vehicle which will stabilize, and carry in the form of an emulsion, drugs which are poorly soluble in lipids and in water.

SUMMARY OF THE INVENTION 45

In order to meet these needs, the present invention is directed to pharmaceutical compositions including: a-tocopherol, a surfactant or mixtures of surfactants, with and without an aqueous phase, and a therapeutic agent 5Q wherein the composition is in the form of an emulsion, mice liar solution or a self-emulsifying drug delivery system. In a preferred form, the solution is substantially ethanol-free.

The pharmaceutical compositions can be stabilized by the addition of various amphiphilic molecules, including 55 anionic, nonionic, cationic, and zwitterionic surfactants. Preferably, these molecules are PEGylated surfactants and optimally PEGylated a-tocopherol.

The amphiphilic molecules further include surfactants such as ascorbyl-6 palmitate; stearylamine; sucrose fatty 60 acid esters, various vitamin E derivatives and fluorinecontaining surfactants, such as the Zonyl brand series and a polyoxypropylene-polyoxyethylene glycol nonionic block copolymer.

The therapeutic agent of the emulsion may be a chemo- 65 therapeutic agent preferably a taxoid analog and most preferably, paclitaxel.

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The emulsions of the invention can comprise an aqueous medium when in the form of an emulsion or micellar solution. This medium can contain various additives to assist in stabilizing the emulsion or in rendering the formulation biocompatible.

The pharmaceutical compositions of the invention are typically formed by dissolving a therapeutic agent in ethanol to form a therapeutic agent solution, a-tocopherol is then added to the therapeutic agent solution to form an a-tocopherol and therapeutic agent solution. Next, the ethanol is removed to form a substantially ethanol-free a-tocopherol and therapeutic agent solution. The substantially ethanol free a-tocopherol and therapeutic agent solution is blended with and without an aqueous phase incorporating a surfactant to form a pre-emulsion. For IV delivery the pre-emulsion is then homogenized to form a fine emulsion. For oral delivery, the pre-emulsion is typically encapsulated in a gelatin capsule.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood by reference to the figures, in which:

FIG. 1A shows the particle size of a paclitaxel emulsion (QWA) at 7° C. over time;

FIG. IB shows the particle size of a paclitaxel emulsion (QWA) at 25° C. over time;

FIG. 2 is an HPLC chromatogram showing the integrity of a paclitaxel in an emulsion as described in Example 5;

FIG. 3A shows the paclitaxel concentration of a paclitaxel emulsion (QWA) at 4° C. over time;

FIG. 3B shows the paclitaxel concentration of a paclitaxel emulsion (QWA) at 25° C. over time; and

FIG. 4 shows the percentage of paclitaxel released over time from three different emulsions. The symbol • represents the percentage of paclitaxel released over time from an emulsion commercially available from Bristol Myers Squibb. The symbol T represents the percentage of paclitaxel released over time from an emulsion of this invention containing 6 mg/ml paclitaxel (QWA) as described in Example 6. The symbol 0 represents the percentage of paclitaxel released over time from an emulsion of this invention (QWB) containing 7 mg/ml paclitaxel as described in Example 7.

DETAILED DESCRIPTION OF THE
INVENTION

To ensure a complete understanding of the invention the following definitions are provided:

a-tocopherol: a-tocopherol, also known as vitamin E, is an organic molecule with the following chemical structure (Scheme I):

Hydrophile-lipophile balance: An empirical formula used to index surfactants. Its value varies from 1-45 and in the case of non-ionic surfactants from about 1-20. In general for lipophilic surfactants the HLB is less than 10 and for hydrophilic ones the HLB is greater than 10.

Biocompatible: Capable of performing functions within or upon a living organism in an acceptable manner, without undue toxicity or physiological or pharmacological effects.

Substantially ethanol-free: A composition having an ethanol concentration less than about 1.0% (w/v) ethanol.

Emulsion: A colloidal dispersion of two immiscible liquids in the form of droplets, whose diameter, in general, are between 0.1 and 3.0 microns and which is typically optically opaque, unless the dispersed and continuous phases are

Various chemical derivatives of vitamin E TPGS including ester and ether linkages of various chemical moieties are included within the definition of vitamin E TPGS.

Polyethylene glycol: Polyethylene glycol (PEG) is a hydrophilic, polymerized form of ethylene glycol, consisting of repeating units of the chemical structure—(CH2— CH2—O—).

AUC: AUC is the area under the plasma concentrationtime, commonly used in pharmacokinetics to quantitate the percentage of drug absorption and elimination. A high AUC generally indicates that the drug will successfully reach the target tissue or organ.

Poloxamers or Pluronics: are synthetic block copolymers of ethylene oxide and propylene oxide having the general structure:

OH (OCH2CH2)a (OCH2CH2CH2)b (OCH2CH2)a H

The following variants based on the values of a and b are commercially available from BASF Performance Chemicals (Parsippany, N.J.) under the trade name Pluronic and which consist of the group of surfactants designated by the CTFA name of Poloxamer 108, 188, 217, 237, 238, 288, 338, 407, 101, 105, 122, 123, 124, 181, 182, 183, 184, 212, 231, 282, 331, 401, 402, 185, 215, 234, 235, 284, 333, 334, 335, and 403. For the most commonly used poloxamers 124, 188, 237, 338 and 407 the values of a and b are 12/20, 79/28, 64137, 141/44 and 101/56, respectively.

Solutol HS-15: is a polyethylene glycol 660 hydroxystearate manufactured by BASF (Parsippany, N.J.). Apart from free polyethylene glycol and its monoesters, di-esters are also detectable. According to the manufacturer, a typical lot of Solutol HS-15 contains approximately 30% free polyethylene glycol and 70% polyethylene glycol esters.

Other surfactants: Other surfactants useful in the invention include ascorbyl-6 palmitate (Roche Vitamins, Nutley N.J.), stearylamine, and sucrose fatty acid esters (Mitsubishi Chemicals). Custom surfactants include those compounds with polar water-loving heads and hydrophobic tails, such as

refractive index matched. Such systems possess a finite 30 stability, generally defined by the application or relevant reference system, which may be enhanced by the addition of amphiphilic molecules or viscosity enhancers.

Microemulsion: Athermodynamically stable isotropically clear dispersion of two immiscible liquids, such as oil and water, stabilized by an interfacial film of surfactant mol

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ecules. The microemulsion has a mean droplet diameter of less than 200 nm, in general between 10-50 nm. In the absence of water, mixtures of oil(s) and non-ionic surfactant (s) form clear and isotropic solutions that are known as self-emulsifying drug delivery systems (SEDDS) and have

40 successfully been used to improve lipophilic drug dissolution and oral absorption

Aqueous Medium: A water-containing liquid which can contain pharmaceutically acceptable additives such as acidifying, alkalizing, buffering, chelating, complexing and

45 solubilizing agents, antioxidants and antimicrobial preservatives, humectants, suspending and/or viscosity modifying agents, tonicity and wetting or other biocompatible materials.

Therapeutic Agent: Any compound natural of synthetic

50 which has a biological activity, is soluble in the oil phase and has an octanol-buffer partition coefficient (Log P) of at least 2 to ensure that the therapeutic agent is preferentially dissolved in the oil phase rather than the aqueous phase. This includes peptides, non-peptides and nucleotides. Lipid

55 conjugates/prodrugs of water soluble molecules are within the scope of therapeutic agent.

Chemotherapeutic: Any natural or synthetic molecule which is effective against one or more forms of cancer, and particularly those molecules which are slightly or com

60 pletely lipophilic or which can be modified to be lipophilic. This definition includes molecules which by their mechanism of action are cytotoxic (anti-cancer agents), those which stimulate the immune system (immune stimulators) and modulators of angiogenesis. The outcome in either case

65 is the slowing of the growth of cancer cells.

Chemotherapeutics include Taxol (paclitaxel) and related molecules collectively termed taxoids, taxines or taxanes.