Background. The field of nanotechnology is growing rapidly, encompassing many disciplines and areas of research. This developing study is widely applicable in the world of medicine, and more specifically, cancer therapeutics. Nanoparticles can be used to target specific cancer cells and deliver a desired payload (i.e. drug, gene) to the cells.

Liposomes are nanoparticles that are commonly chosen for their biocompatibility and biodegradability. Liposomes are spherical nanoparticles consisting of a lipid bilayer surrounding an aqueous environment. These liposomes may be coated with sugars such as hyaluronan, which serve the dual purpose of stabilizing the nanoparticle as well as providing further potential binding sites (Peer et al 2003). These binding sites can be used to conjugate targeting molecules to the nanoparticles, thereby allowing targeted delivery. Additionally, liposomes can be used to entrap various molecules such as siRNA, viruses, or drugs. This can be accomplished by lyophilizing (freeze-drying) the nanoparticles and resuspending them in a solution containing the molecule of interest (Shimaoka et al 2008), rendering these nanoparticles as effective vehicles for delivery (Figure 1).<box 435px full>:labmembers:bl_liposomes.jpg</box|Figure 1. An overview of the surface modification of liposomes and subsequent entrapment of desired molecule.>

<box 170px right>:labmembers:bl_spio_diagram.jpg</box|Figure 2. A depiction of an iron oxide nanoparticle with surface modifications.>Super paramagnetic iron oxide nanoparticles (SPIO) are potentially useful because they serve as contrast agents for magnetic resonance imaging (MRI) (Duguet et al 2004). These nanoparticles can be easily viewed in vivo in a three-dimensional and non-invasive manner. SPIO nanoparticles are made of Fe3O4, also known as magnetite (Palmacci et al 1993). They are easily synthesized and also commercially available. SPIO nanoparticles may also be coated with sugars to confer stability and to generate functional groups on the surface of the nanoparticle for the purposes of conjugating targeting molecules (Figure 2).

Current Work. My current work has focused on the synthesis and characterization of nanoparticles as well as developing the conjugation techniques necessary to attach targeting molecules to the surface of these nanoparticles.

Liposomes are synthesized using a mixture of phosphatidylcholine (PC), dipalmitoylphosphatidylethanolamine (DPPE) and cholesterol, which is eventually pushed through an extruder to form uniform 100 nm nanoparticles.

<box 430px left>:labmembers:bl_spio.jpg</box|Figure 3. A comparison of commercial and synthesized iron oxide nanoparticles.>Initially, iron oxide nanoparticles were synthesized using an ammonium precipitation method as described in Palmacci et al 1993, but without the high pressures and temperatures available in a non-commercial setting, the resulting nanoparticles were non-homogeneous in size (Figure 3). For this reason, we have turned to commercially available iron oxide nanoparticles, which are uniform but not as cost effective. These nanoparticles are available with either carboxyl groups or amine groups on the surface.

We were able to develop effective conjugation techniques using two different chemistries. For carboxyl group chemistry, N-hydroxysulfosuccinimide (Sulfo-NHS) and 1-Ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride (EDC) are used (Pierce 2008). For thiol group chemistry, such as conjugating protein A to nanoparticles, Sulfosuccinimidyl-4-(N-maleimidomethyl)cyclohexane-1-carboxylate (Sulfo-SMCC) is used (Pierce 2008).

Goals. Our current focus is to successfully conjugate hyaluronan to our liposomes and characterize these liposomes for size, surface charge potential, morphology, and various other traits. After characterization, liposomes will be used to encapsulate various diagnostic and delivery molecules. These molecules include Adeno-associated virus 2 (AAV2) (reference other member’s lab pages for background on AAV2) or iron oxide nanoparticles (for viewing by MRI). Our eventual goal is to conjugate a targeting molecule to the outside of the liposomes to allow efficient and effective delivery of the desired payload.

Selected References.

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Cornell School of Chemical and Biomolecular Engineering '10