was prepared with phosphate buffered saline (PBS) and filtered with sterile filters (0.2 µm). At the end of incubation period, 20 µL of MTT solution was added to each well. After 1h incubation, the medium was removed and 200 μL of dimethylsulfoxide (DMSO) was then added to each well to dissolve the formazan crystals. The absorbance was then measured by a microplate reader (LAB Systems Original Multiscan MS) at 570 nm. Cell viability was calculated as the absorbance ratio between treated and untreated control cells. All experiments were performed in triplicate to determine means and SD.