News Column

"Topical Dermal Delivery Compositions Using Self Assembling Nanoparticles with Cetylated Components" in Patent Application Approval Process

September 12, 2014

By a News Reporter-Staff News Editor at Drug Week -- A patent application by the inventors Barathur, Raj R. (Escondido, CA); Bookout, Jack Bain (San Diego, CA), filed on February 15, 2013, was made available online on August 28, 2014, according to news reporting originating from Washington, D.C., by NewsRx correspondents (see also Cymbiotics, Inc.).

This patent application is assigned to Cymbiotics, Inc.

The following quote was obtained by the news editors from the background information supplied by the inventors: "Many new bioactive pharmaceutical compounds have solubility properties that can adversely affect drug bioavailability and efficacy. These compounds frequently lack either sufficient lipophilicity, reduced transdermal transport, or require some form of protective delivery matrix in order to improve performance. To address these issues many advanced delivery systems have been developed to improve solubility and enhance absorption. As a result, a panorama of such advanced delivery systems have evolved, and these approaches include cerasomes, dendrimers, liposomes, lipoids, micelles, nisosomes and polymeric micelles (US patent application 2012/0116064 by Dai, Liang and Yue; U.S. Pat. No. 6,579,906 to Cooper and Chen, issued Jun. 17, 2003; European Patent EP 0036277 to Papahadjopoulos, issued Aug. 28, 1985; U.S. Pat. No. 5,565,213 to Nakamori, Yoshida, et al., issued Oct. 15, 1996; U.S. Pat. No. 4,694,064 to Tomalia and Kirdhhoff, issued Sep. 15, 1987; U.S. Pat. No. 4,830,857 to Handjani, Ribier, et al., issued May 16, 1989). A review of many of these delivery mechanisms is given in Huynh, et al. Nanomedicine: Nanotechnol Biol and Med, 8, pp. 20-36 (2012), which is incorporated herein for reference.

"Many systems derive enhanced attributes through the generation of colloid suspensions with suspended particulates having characteristic dimensions between 1 and 1,000 nm. Some examples of colloidal systems are emulsions, liposomes, microemulsions, multiple and multilayer emulsions, nanocrystal suspensions, solid lipid nanoparticles and polymeric particles [Madene A, Jacquot M, et al., Int J Food Sci Technol, 41, pp. 1-21 (2006); McClements D J, Adv Coll Interface Sci, 174, pp.1-30 (2012); McClements D J, Decker E A, Weiss J, J Food Sci, 72, pp. R109-24 (2007); Muller R H, Gohla S, Keck C M, Eur J Pharm Biopharm, 78, pp. 1-9 (2011)]. However, transdermal delivery efficiency of many of these platforms (such as solid lipid nanoparticles) is reduced by the particle size achieved, which is often over 100 nm in diameter.

"A key feature of many systems is the use of amphiphilic/semi-polar substances that exhibit both hydrophilic head groups and hydrophobic chain regions. In an aqueous environment, micelle particulates form from these amphiphilic substances with the polar regions facing out, interacting electrostatically with the aqueous phase, and the more hydrophobic regions, consisting of the hydrocarbon chains, facing inward. Such conditions are conducive for entrapment of hydrophobic bioactives within the hydrophobic matrix of the particulate structure. In environments where the oil phase is predominant, amphiphilic components reconform with hydrophobic regions external and hydrophilic regions being internalized.

"And depending on the composition of the amphiphilic substances, packing of these molecules can be adjusted to form close packing to that of a looser configuration. In essence the behavior of such particulates can be polyphasic, having different phase configurations based the micelle concentration, composition of the liquid environment and amphiphilic components and temperature. Corkill and Goodman, Adv Colloid Interface Sci, 2, pp. 298-330 (1969) demonstrated that in aqueous solutions containing ampholytic components, the length of the alkyl chain greatly affected the concentration at which micelle formation occurred and the type and number of distinct morphic phases that might occur. The effect of increasing the molecular polarity was found to increase the temperatures necessary for different polymorphic phases to occur. Theoretical models have been developed that reflect the micellar structural phases observed and analyzed using low-angle X-ray diffraction [Lipinski, et al. Adv Drug Deliv Rev, 46, pp. 3-26 (2001); Jorgensen and Duffy, Adv Drug Del Rev, 54, pp. 355-366 (2002); Mannhold and Rekker, Perspect Drug Rev, 18, pp. 1-18 (2000)]. The complexity of conditions necessary to favor different phase formations and then to maintain a stable phase can present challenges to manufacture. The following examples are given to show the concerns with some new delivery systems that should be considered in the use and manufacture of such systems for drug delivery.

"Liposomes, manufactured as vesicles of phospholipid bilayers encapsulating an aqueous space (0.03 -10 um diameter) have shown utility of use with a wide variety of drugs. However, hydrolysis or oxidation can degrade the liposomal integrity [Hunt and Tsang, Int J Pharm, 8, pp. 101-110 (1981)] and stability can be compromised due to aggregation, sedimentation of liposome fusion during storage [Wong and Thompson, Biochemistry, 21, pp. 4133-4139 (1982)]. Cerasomes demonstrate improvements over liposomes in regards to high stability towards surfactant solubilization, long term storage and acid treatment [Cao et al., Chem Commun, 46, pp. 5266-5267 (2010)]

"Niosomes are non-ionic surfactants based multilamellar or unilamellar vesicles in which an aqueous solution of solute(s) is enclosed by a membrane resulted from the organization of surfactant macro-molecule as bilayer. Like liposomes, niosomes are also characterized by problems limiting shelf life due physical stability affected by aggregation, fusion and leaking [Hu and Rhodes, Int J Pharm, 206, pp. 110-122 (2000)].

"Dendrimers also demonstrate potential for use with a wide range of different drug types. However, the system also demonstrates drawbacks in the complexity of dendrimer branch synthesis, the presence of branch defects and difficulties in purification after synthesis [Moses and Moorhouse, Chem Soc Rev, 36, pp. 1249-1262 (2007); Crooks, et al. Topics in Cur Chem, 212, pp. 81-135 (2001)].

"Polymeric micelles are nanoscopic core/shell structures formed by amphiphilic block copolymers. They have good stability and good delivery transdermally. Polymers, however, are inherently heterogeneous and can be associated with changes in toxicity and drug efficacy [Duncan, Nature Reviews, 2, pp. 347-360 (2003)].

"For transdermal delivery to be effective, system efficacy often requires enhancement through the use of penetration enhancers. The teachings from several patents support the premise that most pharmaceutically active substances can be introduced transdermally or intradermally with the use of penetration enhancers [U.S. Pat. No. 4.913,905 to Frankhauser issued April 1990; U.S. Pat. No. 4,917,676 to Heiber, issued April 1990; U.S. Pat. No. 5,032,403 to Sinnreich, issued July 1991]. Other enhancing components often include the addition of surfactants or chemical ingredients that modify skin barrier properties to increase transdermal flux. The relationship of such components and utilizations will be discussed in relation to this invention."

In addition to the background information obtained for this patent application, NewsRx journalists also obtained the inventors' summary information for this patent application: "The invention is based on the discovery of a unique delivery system, which self assembles and is stable once manufactured. The teachings found in U.S. patent application Ser. No. 12,608,963, Barathur and Bookout, submitted Oct. 29, 2009 are incorporated herein, which describe several combinations of cetylated fatty esters and their functions as amphiphilic penetration enhancers. It was initially found that, when combined with polar solvents, certain combinations of cetylated esters with different alkane chain lengths and polar regions could be used to facilitate the transdermal flux of bioactives with properties that affected the efficacy of delivery through the stratum corneum.

"This invention disclosure brings forward the utilization of these cetyl esters in combination with cetylated alcohols, polar solvents and surfactants to form unique nanoparticles or vesicles when suspended within an aqueous media. The particles are characterized by micelle and colloid properties with single particle size ranging from 50 to 850 nm. Because their composition is primarily of cetylated monomers, the particles have been given the designation of term 'cetosomes'. This helps differentiate these particles from uniquely different particles like niosomes, cerasomes, polymeric micelles, dendrimers, liposomes, lipoids, solid lipid nanoparticles and other particles. The definition of cetosome will be described in detail herein.

"By process used and by liquid environment provided, the cetosomes can self-assemble. Cetosomes are generated through phased assemblies as hydrophobic alignments of hydrocarbon chains with polar regions facing out into the aqueous interphase. Interspersed within these vesicular formations and generating an outer corona or mantle region around the core are the polar solvent and solubilizer molecules, which enhance the electrostatic stability with water molecules at the exterior region of the cetosomes. In addition, they also may be incorporated to some degree within the core matrix, which allow for the entry and additional capture of both polar and other hydrophobic bioactive molecules. Cetyl and stearyl alcohols, as defined molar components of the cetosomal matrix, further contribute to the amphiphilic characteristics of the particles and serve as stabilizing components for structural stability. The vesicles are elastic and deformable, yet steric effects favor spherical symmetry. The elasticity is enhanced with edge activators such as surfactants. Surfactants also play a key role in reducing the size of these nanoparticles. They help in the formation of oriented monolayers at interfaces, decrease the size range of the cetosomes, while increasing stability, and provide critical rheological properties to the system.

"A key utilization for this invention was that the cetylated fatty esters, cetyl alcohol and stearyl alcohol have melting points well above product utilization temperatures (i.e., they display a thermal phasic nature which can be exploited for this invention). These molecules when heated in an aqueous environment recombine upon cooling into large globular, waxy masses that cannot serve as penetration agents in this physical state. However, temperature elevation allows for component melting, after which other solubilizing and stabilizing components indicated above can be introduced so that as the temperature is reduced and under appropriate emulsifying conditions a coalescing occurs into uniform microparticles with stable colloid properties, and by this manner macro-solidification is eliminated. Where a more hydrophobic interior core within the cetosome is desired, oils or a relatively nonpolar ingredient can be introduced around which the cetosomes form. Under these conditions, particle size tends to become biphasic with a smaller component (cetosomes with 'empty', possibly more solid core centers) and larger cetosome particles having larger centers containing (with formulation) oil or nonpolar additive. The smaller component is calculated to have a core formed by a minimal number of amphiphilic layers. The larger cetosome centers can be made with increased capacity for hydrophilic drugs through the use of oils containing mixtures of glyceryl polyethylene glycol oxystearate, fatty acid glyceryl polyglyceryl esters and glyceryl ethoxylate. The larger cetosomes demonstrate birefringent characteristics. This feature has the characteristics of liquid crystallization and does not have the properties of solid crystal formation. Particle birefringence is often the result of light bending effects caused by a lamellar internal structure.

"Stability of these cetosomes is due in part to the relatively elevated negative zeta potential (Zp). Factors that contribute to stability include electrostatic interactions between charged groups and oppositely charged groups of surfactants, hydrophobic interactions between the cetosomal agents and the hydrophobic regions of the solvents and surfactants and hydrogen bonding interactions (van der Waals). Stability of the nanoparticles is defined by lack of discernible coalescence or flocculation for periods of 1 month or more after manufacture. The major forms of cetosomes are spherical; however, more complex phase changes can be elicited through modifying composition. The invention has been found to be most efficient for transdermal delivery when the cetosomes are generated in the compact, spherical form.

"Compared with other transdermal delivery systems, the formulations containing cetosomes appear to have increased entrapment capacity and greater surface activity for skin penetration. The cetosomes can serve as drug carriers for a wide range of small molecules, peptides and proteins. The combination of cetosomes within the vehicle delivery system has a distinctive effect on the dermal and transdermal delivery of active ingredients. Due to the complexity of the delivery system, some effects contributing to penetration efficiency are not fully defined. Our system is proposed to provide a maximizing of thermodynamic activity for the permeant while incorporating penetration enhancers that increase diffusivity across the skin. For purpose of this submission, a permeant is defined as a molecular species moving through of moving into the tissue. By definition, a penetrant is a molecular species that facilitates in some manner transdermal penetration of the permeant.

"Cetosomes tend to facilitate penetration through the stratum corneum and underlying viable skin but may tend not to remain intact during the process, releasing into smaller penetration units containing any carried molecules and thereby initiating the process of penetration. The cetylated esters tend to partition in high concentrations on the skin, which provides an increased diffusion rate for drugs of interest. All cetylated fatty esters by definition contain the cetyl alkane chain. In addition to this alkane with its hydrophobic properties, the fatty acid component of these molecules provides further hydrophobicity but also hydrophilic polar components. Fatty acids with no unsaturated alkane regions provide secondary structure that is straight and that can readily intercalate between membrane lipids with least disruption. Fatty acids with double bonding between carbons in a cis-configuration introduce bending in the secondary structure that when intercalated in the membrane lipids, causes greater disruptions in the membrane configuration. These molecules intercalate within the lipid bilayers with several disruptions--rotating, vibrating, translocating, forming microcavities and increasing the free volume available for drug diffusion. Pooling may occur with permeable pores forming which, for polar molecules, provide greater access to viable epidermis. This may be a critical step in allowing diffusion through the gel-like viscosity of the lipid matrix.

"Upon application of vehicle containing the cetosomes to the skin, the fluid phase is drawn by diffusion into the stratum corneum and allows the cetosomes to coalese into larger, fragmenting complexes that concentrate the permeants with the penetration enhancers. The polar solvent and cetylated molecules act in conjunction to allow for rapid absorption and avoid the formation of a waxy film that would slow permeant migration. The primary delivery effect of the cetosome is to move the permeant through the permeation barrier of the stratum corneum to the site desired for utilization of the drug. The structure of the cetylated molecules plays a major role in this permeability process by disrupting the lipid organization of the stratum corneum, increasing the diffusion coefficients of the permeants. Premature drug release is prevented in part through affinities between the drug and core components of the cetosomes, the latter acting as penetrant carriers for controlled release within the dermis and stratum corneum.

"Another critical aspect of this invention is the introduction of functional groups within the cetosome that have heightened affinities for the permeants of interest (i.e., functional groups with polar affinities for more ionic permeants such as diclofenac or with more lipophillic affinities for more non-polar permeants). This is accomplished through the selection of the components for the cetosome assembly and the molar ratio of the components added. 1. Hydrophilic compounds and ionized species (log P.sub.octanol/water.ltoreq.3) require different approaches to penetration than that of more lipophilic chemicals. From the aqueous matrix, these are incorporated within the cetosomes through entrapment during assembly or through introduction of cetylated esters into the cetosome with noncovalent, charged affinities for the drug compound. Additional drug molecules may become associated with the charged corona region around the cetosome. Khalil, Najjar and Sallam, Drug Devel Indust Pharm, 26(4), 375-381 (2000) teach, for example, that different salts of diclofenac exhibit different affinities in relation to micellar positioning. Diclofenac sodium, having greater ionization capacity than diclofenac diethylamine, has a higher potential to be associated with the solvent mantle of micelles, while the latter drug salt has greater affinity for location within the micelle core. Physical properties of the cetosomes appear to establish similar relationships dependent upon the properties of the drug of interest. The cetosomes, however, unlike the micelle, can be compositionally modified to increase core affinity for a drug of interest and still maintain architectural integrity. 2. Lipophilic compounds (log P.sub.octanol/water.gtoreq.3) have natural affinities for incorporation within the cetosome core, creating a hydrophobic microenvironment within an aqueous medium. This is responsible for encapsulating hydrophobic 'guests' and making of the aggregates. Upon skin application, the cetylated molecules in the cetosomes provide more efficient penetration through their affinity for the permeant, complexing as previously noted, and partitioning into the bilayer lipids, disrupting the organized packing but also dispersing within the intercellular lipids to facilitate permeant diffusion.

"Upon application to the skin, cetylated components and other penetrant agents allow for enhanced diffusion of the permeant to proceed at rates which are mediated by the properties of the drug molecules and the composition of the cetosome complex. The composition of the cetosomes also helps to reduce water loss from the stratum corneum, increasing hydration and assisting in diffusion of more ionic permeants.


"FIG. 1 shows a concept schematic of a representative nanoparticle of the invention; a center-filled region [5], encapsulated by a core [11] composed of primarily of cetyl esters, cetyl alcohols, stearyl alcohols and surfactant molecules (structures with a terminal 'S'); a corona/mantle region [20] contains both surfactant molecules and polar solvent molecules (PS); drug of interest (designated as D).

"FIG. 2 shows the zeta potential for the dispersion in composition CLDC0704 as described in Example 1.

"FIG. 3 shows the particle distribution sizes for the dispersion particles formed in composition CLDC0704 as described in Example 1."

URL and more information on this patent application, see: Barathur, Raj R.; Bookout, Jack Bain. Topical Dermal Delivery Compositions Using Self Assembling Nanoparticles with Cetylated Components. Filed February 15, 2013 and posted August 28, 2014. Patent URL:

Keywords for this news article include: Alcohols, Carboxylic Acids, Cyclooxygenase Inhibitors, Cymbiotics, Cymbiotics Inc., Diclofenac, Drug Delivery Systems, Drugs, Emerging Technologies, Esters, Legal Issues, Liposomes, NSAID, Nanoparticle, Nanotechnology, Ophthalmic Antiinflammatory Agents, Ophthalmic Preparations, Organic Chemicals, Phenylacetates, Therapy, Topical Agents, Transdermal.

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Source: Drug Week

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