BackgroundReliable in vitro toxicity testing is needed prior to the commencement of in vivo testing necessary for hazard identification and risk assessment of nanoparticles. In this study, the cytotoxicity and uptake of 14 nm and 20 nm citrate stabilised gold nanoparticles (AuNPs) in the bronchial epithelial cell line BEAS-2B, the Chinese hamster ovary cell line CHO, and the human embryonic kidney cell line HEK 293 were investigated.MethodsCytotoxicity of the AuNPs was assessed via traditional XTT-, LDH-, and ATP-based assays, followed by cell impedance studies. Dark-field imaging and hyperspectral imaging were used to confirm the uptake of AuNPs into the cells.ResultsInterference of the AuNPs with the XTT- and ATP-based assays was overcome through the use of cell impedance technology. AuNPs were shown to be relatively non-toxic using this methodology; nevertheless CHO cells were the most sensitive cell type with 20 nm AuNPs having the highest toxicity. Uptake of both 14 nm and 20 nm AuNPs was observed in all cell lines in a time- and cell type-dependent manner.ConclusionsUsing the cell impedance and dark-field hyperspectral imaging technologies, it was possible to study the toxicity of AuNPs in different cell lines and show that these cells could internalize AuNPs with their subsequent intracellular aggregation. It was also possible to show that this toxicity would not correlate with the level of uptake but it would correlate with cell-type and the size of the AuNPs. Therefore, these two label-free methodologies used in this study are suitable for in vitro studies on the effects of AuNPs, and could present themselves as appropriate and valuable methodologies for future nanoparticle toxicity and uptake studies.

Pyrazoles are widely used as core motifs for a large number of compounds for various applications such as catalysis, agro-chemicals, building blocks of other compounds and in medicine. The attractiveness of pyrazole and its derivatives is their versatility that allows for synthesis of a series of analogues with different moieties in them, thus affecting the electronics and by extension the properties of the resultant compounds. In medicine pyrazole is found as a pharmacophore in some of the active biological molecules. While pyrazole derivatives have been extensively studied for many applications including anticancer, antimicrobial, anti-inflammatory, antiglycemic, anti-allergy and antiviral, much less has been reported on their metal counterparts in spite of the fact that metals have been shown to impart activity to ligands. Thus this perspective is intended to demonstrate the potential of pyrazole and pyrazolyl metal complexes in the areas of drug discovery and development. Several examples, that include palladium, platinum, copper, gold, zinc, cobalt, nickel, iron, copper, silver and gallium complexes, are used to bolster the above point. For the purposes of this review three areas are discussed, that is pyrazole metal complexes as: (i) anticancer, (ii) antibacterial/parasitic and (iii) antiviral agents.

The reactions of potassium salts of the dithiocarbamates L {where L = pyrazolyldithiocarbamate (L1), 3,5-dimethylpyrazolyldithiocarbamate (L2), or indazolyldithiocarbamate (L3)} with the gold precursors [AuCl(PPh3)], [Au2Cl2(dppe)], [Au2Cl2(dppp)], or [Au2Cl2(dpph)] lead to the new gold(I) complexes [AuL(PPh3)] (1–3), [Au2L2(dppe)] (4–6), [(Au2L2)(dppp)] (7–9), and [Au2(L)2(dpph)] (10–12) {where dppe = 1,2-bis(diphenylphosphino)ethane, dppp = 1,3-bis(diphenylphosphino)propane, and dpph = 1,6-bis(diphenylphosphino)hexane}. These gold compounds were characterized by a combination of NMR and infrared spectroscopy, microanalysis, and mass spectrometry; and in selected cases by single-crystal X-ray crystallography. Compounds 4–6, which have dppe ligands, are unstable in solution for prolonged periods, with 4 readily transforming to the Au18 cluster [Au18S8(dppe)6]Cl2 (4a) in dichloromethane. Compounds 1–3 and 7–12 are all active against human cervical epithelioid carcinoma (HeLa) cells, but the most active compounds are 10 and 11, with IC50 values of 0.51 μM and 0.14 μM, respectively. Compounds 10 and 11 are more selective toward HeLa cells than they are toward normal cells, with selectivities of 25.0 and 70.5, respectively. Further tests, utilizing the 60-cell-line Developmental Therapeutics Program at the National Cancer Institute (U.S.A.), showed 10 and 11 to be active against nine other types of cancers.

Collectively, this in vitro study provides insights into action of palladium and platinum complexes and demonstrates the potential use of these compounds, and in particular complex 3, in the development of new anticancer agents.

ABSTRACT

Highly active antiretroviral therapy (HAART) has resulted in decreased mortality and morbidity from the acquired immune deficiency syndrome caused by the human immunodeficiency virus (HIV). Drug resistance and toxicity of HAART has led to the search for novel inhibitors of HIV infection. Gold-based compounds have shown promising activity against a wide range of clinical conditions and microorganism infections including HIV-1. A typical example is auranofin which resulted in an elevated CD4? T-cell count in an HIV patient being treated for psoriatic arthritis. In addition, reports exist on gold-based inhibitors of reverse transcriptase (RT), protease (PR) and viral entry of host cells. These and other characteristics of goldbased HIV drugs are reviewed here.

Surface-modified gold nanoparticles (AuNPs) are nanomaterials that hold promise in drug delivery applications. In this study, the cytotoxicity, uptake, intracellular localization, and the exocytosis of citrate-stabilized (Cit-AuNP) and polyethylene glycol (PEG)-modified gold nanoparticles with the carboxyl (COOH) terminal functional group were assessed in human embryonic kidney (HEK 293) and the human caucasian hepatocytes carcinoma (Hep G2) cell systems, representing two major accumulation sites for AuNPs. The zeta (ζ)-potential measurements confirmed the negative surface charge of the AuNPs in water and in cell growth medium. The transmission electron microscopy confirmed the size and morphology of the AuNPs. Both types of AuNPs were shown to induce cytotoxic effects in cells. The Hep G2 cells were more sensitive cell type, with the COOH-PEG-AuNPs inducing the highest toxicity at higher concentrations. Dark field microscopy and TEM images revealed that the AuNPs were internalized in cells, mostly as agglomerates. TEM micrographs further revealed that the AuNPs were confined as agglomerates inside vesicle-like compartments, likely to be endosomal and lysosomal structures as well as in the cytosol, mostly as individual particles. The AuNPs were shown to remain in cellular compartments for up to 3 weeks, but thereafter, clearance of the gold nanoparticles from the cells by exocytosis was evident. The results presented in this study may therefore give an indication on the fate of AuNPs on long-term exposure to cells and may also assist in safety evaluation of AuNPs.

High affinity thiolate-based polymeric capping ligands are known to impart stability onto nanosized gold nanoparticles. Due to the stable gold-sulfur bond, the ligand forms a protective layer around the gold core and subsequently controls the physicochemical properties of the resultant nanogold mononuclear protected clusters (AuMPCs). The choice of ligands to use as surfactants for AuMPCs largely depends on the desired degree of hydrophilicity and biocompatibility of the MPCs, normally dictated by the intended application. Subsequent surface modification of AuMPCs allows further conjugation of additional biomolecules yielding bilayer or multilayered clusters suitable for bioanalytical applications ranging from targeted drug delivery to diagnostics. In this study, we discuss our recent laboratory findings on a simple route for the introduction of Trans-Activator of Transcription (TAT) peptide onto the surface of biotin-derivatised gold MPCs via the biotin-strepavidin interaction. By changing the surface loading of biotin, controlled amounts of TAT could be attached. This bioconjugate system is very attractive as a carrier in intercellular delivery of various delivery cargoes such as antibodies, proteins and oligonucleotides.