We have developed a novel HDL-based multifunctional platform for transport and delivery of highly hydrophobic gold nanoparticles (AuNP) bearing photothermic properties. We exploit the ability of apolipoprotein E3 (apoE3) to act as a high affinity ligand for the low-density lipoprotein receptor (LDLr) to gain entry into glioblastoma cells. The issue of poor aqueous solubility of AuNP was overcome by integrating them with phospholipids and apoE3, yielding reconstituted rHDL bearing 3, 10, or 10 nm AuNP. UV-Vis spectra of rHDL-AuNP indicated the presence of stable particles with surface plasmon band at ~530 nm, a signature feature of AuNP. Transmission electron microscopy (TEM) revealed discoidal geometry for rHDL with 3, 10 and 17 nm particles. Co-immunoprecipitation assay using a soluble form of the LDLr indicated robust binding of rHDL-AuNP to the receptor. Immunofluorescence analysis indicated that all 3 rHDL particles were internalized by glioblastoma cells, as revealed by the presence of punctate, peri-nuclear endocytic/lysosomal vesicles; this suggests cellular uptake of rHDL-AuNP by receptor-mediated endocytosis. Cellular uptake was further confirmed by TEM, in which aggregated AuNP were found in the endosomal-lysosomal compartments. Finally, cytotoxicity studies demonstrated that more than 50% of cells were viable with rHDL-AuNP treatment of up to 0.1 mg/ml for 24 h. The findings that apoE3: (i) acts as a detergent in solubilizing and dramatically improving the aqueous solubility of AuNP, and, (ii) facilitates cellular uptake of rHDL-AuNP by the LDLr pathway, are significant since they offer an effective means of delivering AuNP across the cell membrane. This is particularly relevant in tumor cells since they overexpress LDLr to meet the high demand for cholesterol that is required for rapid proliferation and membrane biogenesis.
The Interplay of Monolayer Structure and Serum Protein Interactions on the Cellular Uptake of Gold Nanoparticles
