In the present study, interactions of Au(III) and Ga(III) ions on human serum albumin (HSA) were studied. comparatively via spectroscopic and thermal analysis methods: UV-vis absorbance spectroscopy, fluorescence spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and isothermal titration calorimetry (ITC). The potential antitumor effects of these ions were studied on MCF-7 cells via Alamar blue assay. It was found that both Au(III) and Ga(III) ions can interact with HSA, however; Au(III) ions interact with HSA more favorably and with a higher affinity. FT-IR second derivative analysis results demonstrated that, high concentrations of both metal ions led to a considerable decrease in the a-helix content of HSA; while Au(III) led to around 5% of decrease in the a-helix content at 200 mu M, it was around 1% for Ga(III) at the same concentration. Calorimetric analysis gave the binding kinetics of metal-HSA interactions; while the binding affinity (K-a) of Au(III)-HSA binding was around 3.87 x 10(5) M-1, it was around 9.68 x 10(3) M-1 for Ga(III)-HSA binding. Spectroscopy studies overall suggest that both metal ions have significant effects on the chemical structure of HSA, including the secondary structure alterations. Antitumor activity studies on MCF7 tumor cell line with both metal ions revealed that, Au(III) ions have a higher antiproliferative activity compared to Ga(III) ions. (C) 2014 Elsevier GmbH. All rights reserved.