Gold nanoparticles (Au NPs) are being research extensively for various biomedical applications; their applicability arises from a unique set of optical and physical properties brought on by their nanoscale dimensions.1 Furthermore, facile and scalable synthetic and surface functionalization strategies for Au NPs make these properties highly tunable.1 These areas of research are still relatively new and the number of publications per year referring to gold nanomaterials has skyrocketed from 11 in 1990, to 673 in 2000, to more than 31,400 in 2015 (Web of Science database, topic search = “gold nano*”, accessed March 2, 2016). The potential application of Au NPs for disease detection, diagnosis and therapy has motivated numerous analyses of their interactions with biomolecules, cells, animals, humans and the environment.1,2 A vast majority of studies aimed at gaining a better understanding of how cells interact with and are influenced by Au NPs have focused mainly on measuring cytotoxicity and simple cell processes like proliferation or NP uptake. While Au NPs larger than 4-5 nm in diameter (with appropriate, non-toxic surface coatings) have been shown to be largely non-cytotoxic, there can be subtle non-toxic effects induced by Au NPs.3 The adsorption of soluble proteins onto NP surfaces (the protein corona) is highly studied, but little attention has been paid to how those interactions perturb gene expression of cells or to understanding NP interactions with other types of biomolecules. This thesis aims to look deeper into how molecular level effects of NPs in cells and cellular environments can lead to down-stream changes to cell gene expression and behavior. Firstly, the impact of Au nanorods (Au NRs) on 3D cancer cell migration via interactions between Au NRs and extracellular matrix (ECM) structural proteins was examined.4 While experiments on the influence of NPs on cell behaviors exist, nearly all of these studies neglect the impact of the ECM. In vivo cells exist in complex, fibrous 3D environments and series of intricate biochemical, cell-cell and cell-ECM interactions govern behaviors such as migration. Cancer cell migration allows tumor cells to spread and metastasize to new areas of the body, but little is known about how Au NR interaction with the ECM after injection and targeting to tumors may affect this process. The inevitable contact of in vivo Au NRs with the ECM presents a possible source of unintended side effects. In order to study how gold nanoparticles can influence ECM properties and cell-ECM interactions, we have created a nested-gel type I collagen matrix for measuring whether Au NRs alter the migration of MDA-MB-231 human breast cancer cells in 3D collagen environments. In contrast to the few studies of Au NR-induced migration changes in 2D environments, our results show that Au NRs in a model ECM increase the frequency of spontaneous cellular migration. The presence of negatively-charged polyelectrolyte-coated Au NRs during the collagen self-assembly process was shown to induce mechanical and structural changes, to alter molecular diffusion, and to affect cellular adhesion, morphology, locomotion strategy and protease expression. The results demonstrate the indirect impact nanoparticles can exert on cell behaviors within three-dimensional ECMs.The shape and surface chemistry of Au NPs was also investigated in terms of the role of these factors in cellular transcriptomic (gene expression) responses after both short- and long-term exposures.5 Respectively, human dermal fibroblasts (HDF) and prostate cancer (PC3) cells were exposed to 0.1 nM (24 hours) and 1.0 nM (48 hours) concentrations of Au NPs of four different, but related surface chemistries. A combination of microarray gene expression analysis techniques and typical cellular characterization was used to learn more about how the nature of the Au NP surface coating influences cells on a molecular level. Identity, charge and lability of surface coatings (and cell type and dosing parameters) were all implicated as important factors to consider in order to predict gene expression responses. In a separate study, HDF cells were exposed to 0.1 nM (low-dose) Au NPs of different shapes and surface coatings for 20 weeks. The long-term effects of acute (24 hour) and chronic (20 weeks) exposure were measured by viability, proliferation, NP uptake, and morphology studies combined with gene expression analysis of genes related to stress and toxicity pathways. It is rare to find chronic exposure studies, especially with Au NPs, and these experiments showed that acute, sub-cytotoxic doses of NPs may induce long-term stress on cells. These cells were found to react very differently to acute versus chronic doses of the same NPs after 20 weeks. Additionally, surface coating was shown to have a much larger impact on determining NP-cell interactions than shape of Au NPs. In all, we have expanded the collective understanding of the molecular interactions Au NPs experience inside cells based on surface chemistry, shape, dosage and exposure time and parameters.References1. Dreaden, E.C.; Alkilany, A.M.; Huang, X.; Murphy, C.J.; El-Sayed, M.A. The Golden Age: Gold Nanoparticles for Biomedicine. Chem. Soc. Rev. 2012, 41, 2740–2779.2. Yang, X.; Yang, M.; Pang, B.; Vara, M.; Xia, Y. Gold Nanomaterials at Work in Biomedicine. Chem. Rev. 2015, 115, 10410–10488.3. Alkilany, A.M.; Lohse, S.E.; Murphy, C.J. The Gold Standard: Gold Nanoparticle Libraries to Understand the Nano-Bio Interface. Acc. Chem. Res. 2013, 46, 650–661.4. Grzincic, E.M.; Murphy, C.J. Gold Nanorods Indirectly Promote Migration of Metastatic Human Breast Cancer Cells in Three-Dimensional Cultures. ACS Nano 2015, 9, 6801–6816.5. Grzincic, E.M.; Yang, J.A.; Drnevich, J.; Falagan-Lotsch, P.; Murphy, C.J. Global Transcriptomic Analysis of Model Human Cell Lines Exposed to Surface-Modified Gold Nanoparticles: The Effect of Surface Chemistry. Nanoscale 2015, 7, 1349–1362.
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Investigating the impact of gold nanoparticles on cells: from transcription to behavior
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