MTT assay

The viability of cells was estimated using MTT (Sigma Chemical Co., St. Louis, USA) assay described previously⁵³. Briefly, 10 μl of MTT solution (5 mg/ml in ddH₂O) was added to each well. The plates were then incubated for 4 hr at 37 °C. Intracellular formazan crystals were dissolved by addition of 100 μl of isopropanol-HCI-SDS solution to each well. After overnight incubation at 37 °C, the optical density of the samples was determined at 570 nm. Rate of inhibition was calculated by using the equation: Rate of inhibition = (Ac-At)/Ac × 100, where At and Ac represent the absorbance in treated and control cultures, respectively.