  This study aimed to investigate the antitumor effect of ultrasmall gold
nanoparticles (AuNPs), around 3 nm, stabilized by the anionic polysaccharide
gum arabic (GA-AuNPs). The focus was downregulation of cancer hallmarks of
aggressive tumors, using a highly metastatic model of melanoma. We first
demonstrated that GA-AuNPs showed excellent stability under biological
environment. Non-cytotoxic concentrations to seven different cell lines,
including tumorigenic and non-tumorigenic cells, were determined by standard 2D
in vitro assays. Gold concentrations below 2.4 mg L-1 were non-cytotoxic and
therefore chosen for further analyses. Cells exposed to GA-AuNPs were uptaken
by melanoma cells through endocytic processes. Next, we described remarkable
biological properties using non-cytotoxic concentrations of this nanomaterial.
Invasion through an extracellular matrix barrier as well as 3D growth capacity
(anchorage-independent colony formation and spheroids growth) were negatively
affected by 2.4 mg L-1 GA-AuNPs. Additionally, exposed spheroids showed
morphological changes, suggesting that GA-AuNPs could penetrate into the
preformed tumor and affect its integrity. All together these results
demonstrate that side effects, such as cytotoxicity, can be avoided by choosing
the right concentration, nevertheless, preserving desirable effects such as
modulation of key tumor cell malignancy features.
