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Nanodisk: a versatile drug delivery platform


According to the definition from the National Nanotechnology Initiative, nanotechnology refers to research conducted at a nano-scale level which is about 1 to 100 nanometers (nm). Recent years have seen widespread application of nanotechnology in the field of drug delivery. Using nanotechnology, it is possible to package drugs at a nano-scale level to improve bioavailability, increase plasma circulation time and achieve tissue specific drug delivery with concomitant reduction in possible adverse side effects.

Nanodisks (ND) are self assembled nanoparticles comprised of a phospholipid bilayer stabilized by an apolipoprotein "scaffold". ND can be formulated with significant amounts of bioactive agents. The ND architecture is reminiscent of nascent high density lipoprotein (HDL) particles. In the physiological context, nascent HDL picks up excess cholesterol from peripheral tissues and transports it to the liver for excretion or re-use. In vitro, nascent HDL particles can be reconstituted by incubating phospholipid vesicles with apolipoprotein molecules. In reconstituted HDL (rHDL) the phospholipids arrange as a disk-shaped bilayer with two or more apolipoprotein molecules circumscribing the edge of the disk. In recent years rHDL have emerged as a platform for incorporation and transport of hydrophobic and amphipathic biomolecules. To distinguish rHDL loaded with a bioactive agent from physiological HDL we have coined the terminology ND. The focus of my research has been to evaluate ND's ability to function as a vehicle for two different bioactive agents- curcumin, a polyphenol with anti-cancer properties and small interfering RNA (siRNA), novel nucleic acid molecules with enormous therapeutic potential.

Curcumin is water insoluble and oral administration results in poor systemic bioavailability. Hence, the development of a suitable intravenous delivery vehicle is crucial for curcumin's clinical success. Incorporation of curcumin into ND generates a water soluble formulation suitable for intravenous delivery. Compared to free curcumin, curcumin-ND displayed improved cellular uptake of curcumin, which translated into potent biological effects in established tumor cell lines. Strategic use of an apolipoprotein scaffold, known to bind receptors over-expressed on certain tumor cells, caused further improvement in ND mediated curcumin delivery. In other studies, synthetic siRNA mediated silencing of validated disease targets has been shown to improve clinical outcomes in relevant disease models. However, successful therapeutic application of siRNA relies upon the development of a carrier that protects the siRNA molecules from serum nucleases and facilitates their efficient delivery to target tissues, minimizing off-target effects. In my studies I show that an optimum mole percent of a bilayer forming cationic lipid can be included in the ND formulation generating intact nanometer sized positively charged ND (i.e. cationic lipid ND). Cationic lipid ND stably bound 23-mer double stranded oligonucleotides and experiments showed that cationic lipid ND-bound siRNA efficiently knocked down a target gene in hepatocarcinoma cells. Results indicate that cationic lipid ND have the potential to function as a siRNA carrier.

As a delivery vehicle ND possess several advantages. ND components are biocompatible and their assembly is facile. The potential to engineer the apolipoprotein scaffold, in addition to interchangeability of the lipid and scaffold components, makes ND a versatile delivery platform.

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