2012 IR&D Annual Report

Applied Dermal Delivery Nanoformulations, 01-R8321

Principal Investigators
Gianny J. Rossini
Lucy M. Kimmel
Alda E. Flores

Inclusive Dates:  07/11/12 – 11/11/12

Background — Transdermal drug delivery represents a promising alternative to oral, intravascular, subcutaneous and transmucosal routes of delivery. Gels, patches, and creams are the most frequent and effective alternatives to oral delivery, and after an oral route, are the most common way to administer drugs. In addition, transdermal delivery provides convenient and pain-free self-administration for individuals who need daily medications. It eliminates frequent dosing administration and plasma level peaks and valleys associated with oral dosing and injections; dermal delivery can maintain a constant drug concentration even if the drug has a short half-life in blood. Additionally, the transdermal drug delivery market was worth $12.7 billion dollars in 2005 and is expected to reach $32 billion by 2015. Advanced dermal delivery using nanoformulations is the topic of Project 01-8276, "Combined Laser and Medicated Scar Improvement Therapies." The objective of that project is to develop advanced flexible liposomes known as ethosomes, transferosomes and cubosomes, which have been validated for penetration of skin barriers. Flexible liposomes loaded with corticosteroids will be used as an anti-scarring agent to be used in combination with a carbon dioxide fractional ablative laser. The concept is that the ablative laser will produce a micro array of small pores on the skin, providing an ideal dermal drug delivery opportunity for flexible liposomes. During the execution of 01-8276, the project team developed a network of collaborators that have interest in dermal formulations for their drug candidates. The goal of this project is to formulate those drugs and supply the investigators with samples to conduct animal testing and collect preliminary data.

Approach — Flexible liposomes are made by self-assembled nanoprecipitation of lecithin, or similar phospholipids, from an ethanol solution into a nonsolvent designed for the specific drug-lipid combination. Hydrophilic drugs are loaded in the aqueous core compartment and hydrophobic drugs are normally loaded in the lipid compartment. Basic formulation detergents, such as oleic acid, sodium cholate, turocholate and other additives, are added to modify flexibility and stability. Cubosomes, another kind of flexible liposome, are made with waxy lipids and sticky solids such as monoolein plus a starch coating. It was found that a water-soluble, noncohesive starch coating on the waxy lipid prevents agglomeration and allows control of particle size and control-release rates; in addition, the continuous nature of the particles allows dissolution of otherwise hard to dissolve compounds. The third kind of liposome, transferosomes, are made by the classic thin film method where a lipid/chloroform solution is dried in a round bottle to form a thin film, followed by hydration in buffer and reduction of particle size by extrusion in a stack of nanoporous membranes. Flexibility is generated with the use of detergents such as oleic acid and others increasing membrane fluidity and creating disruptions in the liposome membrane. Avoiding the use of cholesterol or other rigid structural components is also important to maximize flexibility of liposomes. Nanoparticles are measured using a photon correlation spectroscopy (PCS) particle analyzer. Flexibility index is measured by extrusion across a nanoporous size membrane under constant nitrogen pressure. Skin permeability is tested using a Franz cell device setup with skin from cadavers obtained under Institutional Review Board (IRB) regulations or most commonly using synthetic membranes that mimic skin permeability. The procedure is started by applying a full load of samples under occlusive conditions and collecting fractions over time and analyzing to measure drug content, usually 7 hours for human skin and 24 hours for synthetic skin. To measure efficacy of formulated drugs on a skin sample, we use a real-time reverse transcription polymerase chain reaction (RT-PCR) technique that allows us to monitor gene expression at the messenger ribonucleic acid (mRNA) level.

Accomplishments — Flexible dermal formulations such as cubosomes, ethosomes, and transferosomes have been prepared and characterized for drug loading, drug release, particle size, drug permeability, and drug efficacy by RT-PCR. Collaborators at national research laboratories will test SwRI's samples using animal models of Leishmaniasis, a dermal parasitic disease. Leishmaniasis is commonly found in many tropical and subtropical countries and is also found in parts of about 88 countries around the world.

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Southwest Research Institute® (SwRI®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 9 technical divisions.