Proliferation assay: Cell proliferation was examined after treatment with the compounds at their indicated concentration with trypan exclusion method using automated cell counter (Vi-CELL™ XR -Beckman Coulter, Fullerton, CA), after every 24 h interval. Annexin V staining: For evaluating apoptosis, 48 h inhibitor treated cells were stained with Annexin V and propidium iodide (PI), following supplier's guidelines (Invitrogen, Carlsbad, CA) and later the stained cells were subjected to FACS (Cytoflex, Beckman Coulter).