• Muir, Benjamin Ward

Abstract

Polar lipids such as glycerol monooleate and phytantriol are known to form various lyotropic phases, when mixed with water. A number of these lipids are FDA approved for use in vivo. The mesophases of interest include a reversed-type bicontinuous cubic phase formed at sufficiently high concentration under physiological conditions (PBS, pH 7.4, 37 ºC) in excess water. The mesophase exhibit extremely complex phase behavior that is sensitive to minor changes in their composition through addition of various additives which makes them an ideal candidate for studying with High-Throughput (HT) techniques. The mesophase can be dispersed to form stable nanoparticles, commonly called ‘cubosomes’ and ‘hexosomes’ in the presence of suitable biocompatible emulsifiers such as the FDA approved pluronic, F-127.In this presentation the preparation of cubosomes loaded with T1 and T2 contrast agents will be discussed.In this work we have used HT techniques throughout the whole research project, from initial synthesis to testing the materials in vivo. Initially, a Chemspeed robot was used to produce the MRI contrast agent, self assembled cubosome nanoparticles in a HT manner. This was done in order to look for optimum loading of the various contrast agent materials that would allow for maximum signal while retaining the complex mesophase liquid crystal structure. We then used synchrotron source SAXS to confirm the presence of cubic/hexagonal phases in the nanoparticle dispersions produced and their stability. A HT screen was then used in a clinical MRI machine to measure the nanoparticle formulations longitudinal and transverse relaxation rates in water. An in vitro HT cell cytotoxicity screening assay was then devised using a flow cytometer to find formulations that were low in toxicity. Finally, the most suitable candidates that passed each screen along the HT production line were injected into rats via femoral vein cannulation for testing their effectiveness at providing MRI contrast in vivo. It was found that incorporation of various contrast agents into the mesophase significantly enhances their relaxation rates compared to when they are neatly dispersed in water. We have been able to produce agents that are well tolerated in animals and produce excellent MRI contrast in vivo. This work highlights the enormous benefit that HT techniques can bring to rapidly speeding up the complex and multi-disciplinary research and development process that is required when such formulations are intended for use in vivo.Ben W. Muira, Brad Moffatc, Danielle F. Kennedya, Durga Acharyaa, Richard A. Evansa, Tracey Hintonb, Lynne Waddingtona, Kim Warka, Hong Wangd, David Wrightd and Gary Egand aCSIRO Materials Science and Engineering,bAustralian Animal Health Laboratories,cMelbourne University, Department of Radiology,dFlorey Neurosciences Institutes, University of Melbourne,

Topics

• nanoparticle
• impedance spectroscopy
• dispersion
• phase
• toxicity
• small angle x-ray scattering
• liquid crystal