To detect cells undergoing apoptosis, in situ labeling of the 3′ OH end of the DNA fragments generated during apoptosis was performed using the In Situ Cell Death Detection Kit (TUNEL) (Roche Diagnostics, Switzerland) according to the manufacturer’s instructions. Briefly, NCI-H460 cells in their log phase were treated with the culture extract at its IC50 value and incubated for 24 h. Subsequently, culture medium was removed and cells were washed with PBS, air-dried and fixed with 4% paraformaldehyde (in PBS) for 1 h at 25 °C. Fixed cells were washed 3 times with PBS and incubated with permeabilization solution (1% Triton-X in 1% sodium citrate) for 2 min at 4 °C. As a positive control, NCI-H460 cells were fixed, permeabilized and treated with recombinant DNAase I (New England Biolabs, USA) for 10 min to induce DNA strand nicks. Both control and treated cells were washed twice with PBS, and then 50 µL of TUNEL reaction mixture was added to each well. The cells were incubated for 1 h at 37 °C in a humidified dark chamber and subsequently washed three times with PBS and observed under a fluorescence microscope.