At designated time point medium in assay wells of 96-well cell culture plates was replaced with equal volume (100 µL) of the 0.5 mg/mL MTT solution in phenol free complete culture medium. The plates were incubated for 3 hours at 37°C, 5% CO2. Upon incubation the medium was carefully removed and formazan crystals were solubilized with 100 µL DMSO for 10 minutes on orbital shaker at 300 rpm. Absorbance was measured with Tecan Spark 10M microplate reader (Tecan Trading AG, Switzerland) at 500 nm and a reference wavelength of 650 nm. The percentage of cell viability was determined using following formula: (OD 500 sample/OD500 control)*100.