Effects of bisphosphonate ligands and PEGylation on targeted delivery of gold nanoparticles for contrast-enhanced radiographic detection of breast microcalcifications.

A preclinical murine model of hydroxyapatite (HA) breast microcalcifications (µcals), which are an important clinical biomarker for breast cancer detection, was used to investigate the independent effects of high affinity bisphosphonate (BP) ligands and a polyethylene glycol (PEG) spacer on targeted delivery of gold nanoparticles (Au NPs) for contrast-enhanced radiographic detection. The addition of BP ligands to PEGylated Au NPs (BP-PEG-Au NPs) resulted in five-fold greater binding affinity for targeting HA µcals, as expected, due to the strong binding affinity of BP ligands for calcium. Therefore, BP-PEG-Au NPs were able to target HA µcals in vivo after intramammary delivery, which enabled contrast-enhanced radiographic detection of µcals in both normal and radiographically dense mammary tissues similar to previous results for BP-Au NPs, while PEG-Au NPs did not. The addition of a PEG spacer between the BP targeting ligand and Au NP surface enabled improved in vivo clearance. PEG-Au NPs and BP-PEG-Au NPs were cleared from all mammary glands (MGs) and control MGs, respectively, within 24-48 h after intramammary delivery, while BP-Au NPs were not. PEGylated Au NPs were slowly cleared from MGs by lymphatic drainage and accumulated in the spleen. Histopathology revealed uptake of PEG-Au NPs and BP-PEG-Au NPs by macrophages in the spleen, liver, and MGs; there was no evidence of toxicity due to the accumulation of NPs in organs and tissues compared with untreated controls for up to 28 days after delivery. STATEMENT OF SIGNIFICANCE: Au NP imaging probes and therapeutics are commonly surface functionalized with PEG and/or high affinity targeting ligands for delivery. However, direct comparisons of PEGylated Au NPs with and without a targeting ligand, or ligand-targeted Au NPs with and without a PEG spacer, on in vivo targeting efficiency, biodistribution, and clearance are limited. Therefore, the results of this study are important for the rationale design of targeted NP imaging probes and therapeutics, including the translation of BP-PEG-Au NPs which enable improved sensitivity and specificity for the radiographic detection of abnormalities (e.g., µcals) in women with dense breast tissue.

Preparation of fluorescent Au-SiO2 core-shell nanoparticles and nanorods with tunable silica shell thickness and surface modification for immunotargeting.

Gold-silica (Au-SiO2) core-shell nanoparticles (NPs) enable multifunctional properties for in vivo biomedical applications. However, scalable synthesis methods are lacking for the preparation of Au-SiO2 core-shell NPs less than 30 nm in overall diameter with a tunable silica shell less than 10 nm in thickness. Therefore, we prepared monodispersed Au-SiO2 core-shell NPs less than 30 nm in overall diameter with a uniform, tunable silica shell ∼1 to 14 nm in thickness using either citrate reduction followed by a modified Stöber method or oleylamine reduction followed by a reverse microemulsion method. Oleylamine reduction enabled up to 80-fold greater concentration yield compared to the citrate reduction method currently used for synthesizing Au core NPs. The formation of a tunable silica shell less than 10 nm in thickness was facilitated by controlling the molecular weight of the priming polymer (modified Stöber) or surfactant (reverse microemulsion) in addition to the concentration of the silane precursor, and was robust for encapsulating non-spherical morphologies such as Au nanorods. The reverse microemulsion method enabled several distinct advantages over the modified Stöber method, including greater control over the silica shell thickness, ∼16-fold greater yield in core-shell NP concentrations for scalable synthesis, and the ability to encapsulate controlled concentrations of a molecular payload (e.g., fluorophores with four different emission profiles) in the silica shell. Au-SiO2 core-shell NPs were also bioconjugated with immunoglobulin-G (IgG) as a model antibody to demonstrate immunotargeting. Bioactivity of Au-SiO2-IgG core-shell NPs was confirmed by agglomeration in the presence of protein A. The presence and proper orientation of IgG on NP surfaces was verified by direct observation in electron microscopy after negative staining. Therefore, the methods in this study for preparing and modifying Au-SiO2 core-shell NPs provide a platform for engineering core-shell NPs with size-dependent functional properties for multispectral/multimodal imaging, drug delivery, and combined theranostics.