(TEM). The viability, apoptosis, cell cycle distribution and invasive capacity of SW579 cells were assessed following treatment with Au-NPs using a Cell Counting Kit-8 assay, flow cytometric analysis and a Transwell as well as a fluo-

The present study reported on an intrinsic property of gold nanoparticles (Au-NPs), namely their ability to inhibit the proliferation and invasion of thyroid carcinoma cells. Au-NPs of various sizes (5-60 nm) were synthesized and their uptake into the SW579 human thyroid carcinoma cell line was verified using transmission electron microscopy (TEM). The viability, apoptosis, cell cycle distribution and invasive capacity of SW579 cells were assessed following treatment with Au-NPs using a Cell Counting Kit-8 assay, flow cytometric analysis and a Transwell as well as a fluorometric invasion assay. TEM demonstrated that all sizes of Au-NPs could be taken up by the SW579 cells. The results showed that small-sized Au-NPs (5 and 10 nm) significantly suppressed the proliferation and invasion of SW579 cells and induced apoptosis as well as cell cycle arrest in G0/G1 phase, while larger-sized gold nanoparticles (20-60 nm) did not exert these effects, therefore suggesting that the effects of Au-NPs on SW579 cells were highly associated with their particle size. The reduction of the invasive capacity of SW579 cells following treatment with Au-NPs may be attributed to decreases in the expression of matrix metalloproteinase-2 and -9, which were observed using western blot and reverse-transcription quantitative polymerase chain reaction analyses. The present study was the first to demonstrate that small-sized Au-NPs inhibit the proliferation and invasion of thyroid carcinoma cells, which may contribute to the advancement of biomedical applications of Au-NPs.