The proliferation assay was performed using a MTT toxicology assay kit. The cell culture media were replaced by serum-free cell culture media containing 10 vol% MTT reagent and introduced to each cell culture well and to another one without cells (control), before maintaining the plate at 37°C for 3 h incubation. 100 µL of MTT solubilization solution was added in each well, and the plate was gently mixed at room temperature for 15 min, protected from light. A microplate reader (Biotek Synergy HT) was used to measure the absorption of the solutions at 570 nm, and at 690 nm for subtraction.