Farnesyltransferase inhibitor BMS-214662 induces apoptosis in myeloma cells through PUMA up-regulation, Bax and Bak activation, and Mcl-1 elimination.

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 DeltaPsi(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.