Introduction: Chemotherapy efficacy is limited by toxicity and non-uniform tumor exposure. Liposomal drug carriers are nano-scale, spherical particles with a phospholipid bilayer surrounding an aqueous core. With increased circulation and improved tumor deposition due to the enhanced permeability and retention effect, liposomes increase treatment efficacy and reduce toxicity. However, a lack of understanding regarding tumor growth and metastasis is a challenge for developing treatments. Much current research is devoted to understanding what processes cause tumor behavior. Theranostics, or carriers that combine diagnostic and therapeutic capabilities in one unit, are used to study tumor operation in treatment.
We hypothesized that composite systems, encapsulating gold nanoparticles within liposomes, may be used to improve drug delivery and permit non-invasive imaging. We previously designed a novel gold-lipidic nanocomposite to capitalize on the drug delivery capabilities of liposomes and the imaging contrast power of gold nanoparticles. Here we present the formulation of nanocomposites comprised of 2 nm gold clusters encapsulated within pegylated, long-circulating “stealth” liposomes (Au-LNC).
Materials and Methods: Gold clusters 2 nm in diameter were synthesized in the lab through a modified Brust-Schiffrin method. Two different types of clusters were studied, one capped with glutathione (G-AuNP) and one capped with mercaptosuccinic acid (MSA-AuNP), and both types of clusters were water-soluble. Liposomes were prepared using a dry film hydration method with 9:5:1 molar ratio of 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC), cholesterol, and ,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(poly(ethylene glycol))-2000 (DSPE-PEG 2000) respectively. The lipids were originally dissolved in chloroform, and the chloroform was removed and a thin film was formed through rotary vacuum evaporation. To form Au-LNCs, the thin lipid film was hydrated with aqueous solution containing gold clusters at the desired concentration. The liposomes were sized through extrusion through a 0.8 μm membrane, and unencapsulated gold particles were removed via dialysis.
Physical and pharmacodynamic studies were completed using atomic absorption spectroscopy (gold quantification), dynamic light scattering (size distribution), zeta potential (particle stability), and MTT and SRB assays (cytotoxicity), and in vivo fluorescence/bioluminescence/X-ray images were taken using In Vivo Imaging System (IVIS).
Results and Discussion: The nanocomposites have a high gold encapsulation efficiency, with the final composites showing an average encapsulation efficiency of 66 percent and 54 percent for G-AuNPs and MSA-AuNPs, respectively. The composites show narrow size distribution centered at 100 nm, exhibit minimal cytotoxicity at biologically relevant concentrations, and are readily taken up by PC-3 human prostate cancer cells in vitro.
Conclusions: These data support our hypothesis that gold-lipidic nanocomposites can be prepared and justify preclinical in vivo studies in murine models of human tumors to improve cancer detection and treatment. On-going research with these systems includes determining the effect of the gold nanoparticles on doxorubicin loading and release. Future aims are to continue examining Au-LNCs in treated animals by multispectral optoacoustic tomography (MSOT).