Abstract

We have studied the mechanism of apoptosis elicited by the farnesyltransferase inhibitor (R)-7-cyano-2,3,4,5-tetrahydro-1-(1H-imidazol-4-ylmethyl)-3-(phenylmethyl)-4-(2-thienylsulfonyl)-1H-1,4-benzodiazepine (BMS-214662) in human myeloma cell lines. Low concentrations of BMS-214662 efficiently inhibited protein farnesylation but did not affect the activation of Akt. BMS-214662 treatment increased levels of the BH3-only protein PUMA; induced proapoptotic conformational changes of Bax and Bak; reduced Mcl-1 levels; caused mitochondrial transmembrane potential loss; induced cytochrome c release, caspase activation, apoptosis-inducing factor (AIF) nuclear translocation, and phosphatidylserine exposure; and allowed the development of apoptotic morphology. Western blot analysis of cell extracts revealed the activation of caspases 2, 3, 8, and 9 upon treatment with BMS-214662. The general caspase inhibitor Z-VAD-fmk significantly prevented BMS-214662–induced death in U266 and RPMI 8226 cells but not in NCI-H929 cells. A mixture of selective caspase inhibitors for caspases 9 [N-benzyloxycarbonyl-Leu-Glu-His-Asp-fluoromethyl ketone (Z-LEHD-fmk)], 3 (Z-DEVD-fmk), and 6 (Z-VEID-fmk) approached the protective effect of Z-VAD upon cell death. However, Z-VAD-fmk did not prevent BMS-214662–induced Bax and Bak activation and decrease of Mcl-1 levels. According to its effect on cell death, Z-VAD-fmk inhibited nuclear translocation of AIF in RPMI 8226 and U266 but not in NCI-H929 cells. These results suggest that apoptosis triggered by BMS-214662 is initiated by a PUMA/Bax/Bak/Mcl-1–dependent mechanism. In some cell lines, Bax/Bak activation is not sufficient per se to induce mitochondrial failure and release of apoptogenic proteins, and so caspases need to be activated to facilitate apoptosis. After ΔΨ_m loss, execution of apoptosis was performed in all cases by a cytochrome c-enabled, caspase-9–triggered, caspase cascade and the nuclear action of AIF.