Au/Ag bimetallic nanoparticles (BNPs) exhibit a wide range of excellent electronic, chemical, biological, mechanical and thermal properties due to synergistic effects. However, critical questions regarding stability, biocompatibility and their cytotoxic effects remain to be answered. In this study, Ag/Au BNPs have been synthesized as "alloy" via a chemical reduction method using double molar excess of tryptophan [ν(M):ν(Trp) = 1:2]. We then estimated their toxicity in HCT116, 4T1, HUH7 and HEK293 cell lines in monocellular and spheroid cultures. Ag/Au nanoparticles with metal ratio 3:1, had the maximal antitumor effect in cancer cell lines, while the toxicity was found significantly decreased in non-cancerous cell lines. Our results were also compared to previous data regarding Ag/Au using single molar excess of tryptophan [ν(M):ν(Trp) = 1:1], suggesting that tryptophan has a protective effect on HEK293 and not in cancer cells. Aiming to investigate the molecular mechanism behind nanopartricles cytotoxicity, we studied the expression of cell cycle and apoptosis related genes on HCT116, 4T1, and HUH7 monocellular culture. Hence, we showed that bimetallic cytotoxicity is mediated via the caspase and the p53/Bax/Bcl-2 apoptotic pathway. In conclusion, our study suggests tryptophan ratio along with metal ratio used in Ag/Au BNPs as a successful way to control the toxicity in cancer cells towards non-cancerous cells, underlying the potency of bimetallic nanoparticles as selective anti-tumor agents.
Keywords: Apoptosis; bimetallic; cytotoxicity; gold; nanoparticles; silver.