Short Communication Cellular transport pathways of polymer coated gold nanoparticles I-Chun Lin, BSc a , Mingtao Liang, PhD a,b , Tzu-Yu Liu, MSc a , Michael J. Monteiro, PhD c , Istvan Toth, PhD a,b, ⁎ a School of Chemistry and Molecular Bioscience, University of Queensland, Brisbane, Australia b School of Pharmacy, University of Queensland, Brisbane, Australia c Australian Institute for Bioengineering and Nanotechnology, University of Queensland, Brisbane, Australia Received 26 July 2011; accepted 25 September 2011 Abstract The different transport pathways of 5-nm polymer-coated gold nanoparticles (Au NPs) crossing epithelial Caco-2 cell monolayers were explored. We found that the majority of cationic and neutral Au NPs depended heavily on endocytosis for cellular uptake and transport, and the anionic charged nanoparticles trafficked preferentially through the tight junctions (i.e., a paracellular pathway). The current study demonstrates that the surface chemistry of neutral polymer coatings dictate the trafficking through Caco-2 cell monolayers; poly(ethylene glycol)-coated Au NPs traffic via an endocytosis pathway assisted by microtubules; poly(2,3-hydroxy-propylacrylamide)-coated Au NPs traffic via endocytosis but assisted by other nonmicrotubular pathways. The Au NPs coated with poly(N-isopropylacrylamide) (hydrophobic above the lower critical solution temperature of 32°C) traffic via either the microtubule-assisted endocytosis pathway or the paracellular pathway depending on the temperature. This knowledge will aid in the future of the design of nanoparticles as potential oral drug carriers. From the Clinical Editor: The authors examined different transport pathways of polymer-coated gold nanoparticles to cross epithelial Caco- 2 cells, concluding that surface chemistry of neutral polymer coatings dictates the trafficking through monolayers. © 2012 Elsevier Inc. All rights reserved. Key words: Polymer-coated nanoparticles; Gold nanoparticles; Caco-2 cells; Cellular transport; Endocytosis Understanding the interaction of polymeric nanoparticles with intestinal epithelial cells is imperative for their development as potential oral drug carriers. However, little is known about the effect of nanoparticle size and surface properties on their cellular transport behaviors for such systems. We previously studied the transport of model polymer nanoparticles, made from gold nanoparticles (Au NPs) coated with a dense polymer shell bearing cationic, anionic, or neutral (hydrophilic, hydrophobic) side chain functionalities, across epithelial Caco-2 cells in vitro with sizes ranging from 5 to 20 nm. 1,2 The smaller and neutral nanoparticles showed the highest transport efficiency across the cell monolayer, whereas the larger nanoparticles with hydrophobic or cationic surface properties showed little or no cellular translocation, being mostly trapped inside endocytic vesicles within the cells. In the present study, we sought to unravel the different mechanisms involved in nanoparticle cellular transport by investigating the different transport pathways of 5-nm Au NPs coated with a wide range of polymers (Figure 1) to cross epithelial Caco-2 cell monolayers. By decreasing the temperature to 4°C, we inhibit the endocytosis pathway and thus differentiate between endocytosis and paracellular pathways (transport through tight junctions). 3 If transportation is via the endocytosis pathway, the addition of colchicine (which irreversibly binds to tubulin subunits and blocks the microtubular-assisted endocyto- sis) will further differentiate the type of endocytosis pathway. 4 Microtubules, part of the cytoskeleton, structurally consist of polymer globular tubulin subunits that form an extensive network throughout the cell cytoplasm and can help to generate specific endocytic invaginations at the cell membrane. They have been shown to be responsible for the intracellular trafficking of endocytic vesicles across cells. 5 Studying the endocytic mechanisms of polymer nanoparticles would improve their design as oral drug carriers. Methods The synthesis of polymer-coated 5-nm Au NPs and their physicochemical characterization are detailed elsewhere. 1,2 The This work was supported by the Australian Research Council (DP878733). ⁎ Corresponding author: School of Chemistry and Molecular Bioscience, Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane QLD 4072, Australia. E-mail address: i.toth@uq.edu.au (I. Toth). BASIC SCIENCE Nanomedicine: Nanotechnology, Biology, and Medicine 8 (2012) 8 – 11 nanomedjournal.com 1549-9634/$ – see front matter © 2012 Elsevier Inc. All rights reserved. doi:10.1016/j.nano.2011.09.014 Please cite this article as: I.-C. Lin, M. Liang, T.-Y. Liu, M.J. Monteiro, I. Toth, Cellular transport pathways of polymer coated gold nanoparticles. Nanomedicine: NBM 2012;8:8-11, doi:10.1016/j.nano.2011.09.014