Title of Abstract Development of Gold-Lipid Nanocomposites as a Theranostic Platform
Connor S. Dobson1,2, Christina M. Pickering1,2, Allan E. David2, Peter Panizzi1, Robert D. Arnold1
1 Department of Drug Discovery and Development, Harrison School of Pharmacy and
2 Department of Chemical Engineering, Samuel Ginn College of Engineering, Auburn University, Auburn, AL
Introduction: Chemotherapeutic drugs such as doxorubicin are cytotoxic agents that are effective at killing cancer cells, but are also toxic to healthy cells. Stealth liposome nanoparticles have been used as an effective strategy for improving drug delivery and limiting systemic toxicity, but can still suffer from inconsistencies in formulation, sub-optimal drug release and poor detection in vivo. We hypothesized that it would be possible to use a solvent injection method to create novel nanocomposite systems that consist of encapsulated gold nanoparticles within liposomes to improve drug delivery while also permitting non-invasive imaging.
Materials and Methods: Gold nanoparticles were synthesized by mixing chloroauric acid and either mercaptosuccinic acid or glutathione in a solvent composed of water and methanol, followed by sodium borohydride reduction. The resulting particles were characterized by dynamic light scattering (particle size) and UV-Vis spectroscopy (optical properties). Nanocomposites were formed by hydrating a lipid film in a solution of the AuNP. We examined the in vitro cytotoxicity of both the AuNP and the nanocomposites using mitochondrial enzymatic (MTT) and total protein (SRB) assays, which were used to analyze the potential growth inhibition in human prostate carcinoma (PC-3) cells. The intracellular uptake into PC-3 cells was examined by labeling the nanocomposites with DiR, a non-exchangeable fluorescent membrane probe. Tumor and tissue biodistribution in vivo was performed in athymic NCR mice using a human xenograft model by labeling the nanocomposites with DiR and dosing via tail vein injection, followed by imaging 48 hours post-treatment. A Steglich esterification using EDC and DMAP was used to examine the ability to bind both paclitaxel and doxorubicin to the AuNP.
Results and Discussion: AuNP with diameters of approximately 2-4 nm were synthesized using the method described above. It was shown that the AuNP could be stably entrapped within conventional liposomes to form nanocomposites while maintaining a narrow liposome size distribution profile around 100 nm and a zeta potential near 30 mV, indicating good colloidal stability. In vitro studies indicate that the nanocomposites are non-toxic up to millimolar concentrations and intracellular uptake of the nanocomposites was confirmed by scanning confocal microscopy using the DiR label. Nuclear magnetic resonance (NMR) data indicate that simple carboxyl activation can be used to bind poly-(ethylene glycol), or PEG, to the surface of the gold nanoparticles at room temperature. Preliminary data also suggests that paclitaxel can be bound to the gold nanoparticles via Steglich esterification, but these studies are on-going. Imaging data using an IVIS Lumina indicate that the nanocomposites can be tracked in vivo using a fluorescent membrane probe. However, initial studies (without optimization) indicate that the AuNP can only be detected with mild tissue penetration.
Conclusions: We have developed and characterized a novel gold-lipid nanocomposite consisting of 2-nm AuNP entrapped within liposomes. These particles are readily taken up even by aggressive, hormone-refractory prostate cancer cells and the data suggest that they possess similar tumor deposition properties in vivo compared to traditional long-circulating sterically stabilized liposome (SSL) formulations. Future work will focus on the conjugation of targeting moieties to the nanocomposites as well as the stable, acid-labile linkage of chemotherapeutic drugs to the AuNP in order to achieve controlled release of the drugs at the tumor site for more effective therapy. We will also seek to exploit the optical properties of the gold nanoparticles for simultaneous imaging using multispectral optoacoustic tomography (MSOT).
Acknowledgements: (Optional) This project was funded, in part, by NIH grant 1R01-1EB016100-01 (RDA) as well as the Auburn University Undergraduate Research Fellowship Program (CSD and CMP).