**2.3 Assays for in vitro cytotoxicity**

Cytotoxic effects of plant extracts were measured by using the MTT (3-[4, 5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide; Sigma) assay. Cells were seeded onto a 96 well plate (30,000 cells/well), allowed to attach overnight, and then exposed to five different concentrations of plant extracts for 24, 48, and 72 h. MTT solution dissolved in PBS (40 μl/well) was added. Cells were incubated at 37°C for 4 h. Formazan crystals were dissolved in 160 μl DMSO (dimethyl sulfoxide) at 37°C for 1 h. The plate was read on ELISA reader at 570 nm reference of 690 nm (μQuant, Bio-tek) [32].
