CASP9 and lung cancer: Furthermore, to delineate the contribution of caspases in FDN-mediated apoptosis in lung cancer, A549 cells were pretreated for 2 h with Z-DEVD-FMK (caspase-3 inhibitor) and Z-LEHD-FMK (caspase-9 inhibitor) prior to treatment with FDN (50–200μM) for 24 h.