Stable aqueous dispersions of citrate-stabilized gold nanorods (cit-GNRs) have been prepared in scalable fashion by surfactant exchange from cetyltrimethylammonium bromide (CTAB)-stabilized GNRs, using polystyrenesulfonate (PSS) as a detergent. The surfactant exchange process was monitored by infrared spectroscopy, surface-enhanced Raman scattering (SERS), and X-ray photoelectron spectroscopy (XPS). The latter established the quantitative displacement of CTAB (by PSS) and of PSS (by citrate). The Cit-GNRs are indefinitely stable at low ionic strength, and are conducive to further ligand exchange without loss of dispersion stability. The reliability of the surface exchange process supports the systematic analysis of ligand structure on the hydrodynamic size of GNRs, as described in a companion paper.

Nanomedicine-based approaches to cancer treatment face several challenges that differ from those encountered by conventional medicines during clinical development. A systematic exploration of these issues has led us to identify the following needs and opportunities for further development: (1) robust and general methods for the accurate characterization of nanoparticle size, shape, and composition; (2) scalable approaches for producing nanomedicines with optimized bioavailability and excretion profiles; (3) particle engineering for maintaining low levels of nonspecific cytotoxicity and sufficient stability during storage; (4) optimization of surface chemistries for maximum targeted delivery and minimum nonspecific adsorption; (5) practical methods for quantifying ligand density and distributions on multivalent nanocarriers; and (6) the design of multifunctional nanomedicines for novel combination therapies with supportable levels of bioaccumulation.

Polyethylene glycol (PEG) derivatives were conjugated onto the Cys-34 residue of human serum albumin (HSA) to determine their effects on the solubilization, permeation, and cytotoxic activity of hydrophobic drugs such as paclitaxel (PTX). PEG(C34)HSA conjugates were prepared on a multigram scale by treating native HSA (n-HSA) with 5- or 20-kDa mPEG-maleimide, resulting in up to 77% conversion of the mono-PEGylated adduct. Nanoparticle tracking analysis of PEG(C34)HSA formulations in phosphate buffer revealed an increase in nanosized aggregates relative to n-HSA, both in the absence and presence of PTX. Cell viability studies conducted with MCF-7 breast cancer cells indicated that PTX cytotoxicity was enhanced by PEG(C34)HSA when mixed at 10:1 mole ratios, up to a two-fold increase in potency relative to n-HSA. The PEG(C34)HSA conjugates were also evaluated as PTX carriers across monolayers of HUVEC and hCMEC/D3 cells, and found to have nearly identical permeation profiles as n-HSA.

The stability and hydrodynamic size of ligand-coated gold nanorods (GNRs; aspect ratio 3.6) have been characterized by nanoparticle tracking analysis (NTA)—a single-particle counting method that can measure size distributions with low nanometer resolution. Stable aqueous suspensions of citrate-stabilized GNRs (cit-GNRs) are amenable to surface functionalization without loss of dispersion control. Cit-GNRs can be treated with chemisorptive ligands (thiols and dithiocarbamates), nonionic surfactants (Tween 20), and proteins (human serum albumin), all of which produce stable suspensions at low surfactant concentrations. The precision of NTA (relative standard deviation 10–12%, standard error <2%) is sufficient to allow differences in the hydrodynamic size of coated GNRs to be interpreted in terms of surfactant structure and conformation.

Aim The synergistic effects of gold nanorod (GNR)-mediated mild hyperthermia (MHT; 42–43°C) and cisplatin (CP) activity was evaluated against chemoresistant SKOV3 cells in vitro and with a tumor xenograft model. Materials & methods In vitro studies were performed using CP at cytostatic concentrations (5 μM) and polyethylene glycol-stabilized GNRs, using near-infrared laser excitation for MHT. Results The amount of polyethylene glycol-GNRs used for environmental MHT was 1 μg/ml, several times lower than the loadings used in tumor tissue ablation. GNR-mediated MHT increased CP-mediated cytotoxicity by 80%, relative to the projected additive effect, and flow cytometry analysis suggested MHT also enhanced CP-induced apoptosis. In a pilot in vivo study, systemically administered polyethylene glycol-GNRs generated sufficient levels of MHT to enhance CP-induced reductions in tumor volume, despite their heterogeneous distribution in tumor tissue. Conclusion These studies imply that effective chemotherapies can be developed in combination with low loadings of nanoparticles for localized MHT.