RESUMO
Aim: To investigate the promoting effect of Bcl-2/Bcl-xL inhibitor ABT-737 on apoptosis of gastric cancer cells induced by small molecule Mcl-1 inhibitor UMI-77, and to explore its possible mechanism. Methods: The response of gastric cancer MGC-803 and HGC-27 cells to different concentrations of UMI-77 was detected by MTS assay. In the UMI-77-resistant cell lines, the effect of treatment with UMI-77/ABT-737 alone or in combination on cell viability was detected by MTS assay. The apoptotic rate and the changes of the mitochondrial membrane potential were analyzed by flow cytometry. The cleavage of caspase-9, caspase-3 and PARP-1, as well as the expression level of Bcl-2 family members and IAP proteins, were determined by Western blot. Results: Compared with MGC-803 cells, HGC-27 cells were resistant to UMI-77. Treatment with ABT-737 alone in HGC-27 cells also induced minimal level of cell death. While treatment with both agents induced much greater decreased cell viability. All the dead cells were positive for Annexin V and mitochondrial membrane potential collapsed. Caspase-9, caspase-3 and its substrate PARP-1 were cleaved. All of these proved that the sensitization effect was achieved by activating the mitochondrial apoptotic pathway. Protein levels of XIAP, cIAP1 and cIAP2 decreased after treatment with UMI-77 plus ABT-737. It also resulted in the increase of NOXA and Bcl-2 along with the decline of PUMA and Mcl-1. Conclusions: The combination of UMI-77 and ABT-737 could significantly increase the sensitivity of gastric cancer cells to the Mcl-1 small molecule inhibitor UMI-77.
RESUMO
Objective To investigate the mechanism of apoptosis induced by UMI-77 , a novel selective inhibitor of Mcl-1, in gastric cancer MGC-803 cells. Methods MGC-803 cells were treated with UMI-77 in different concen-trations for 24 h, apoptotic rates were determined by Annexin V/PI method using flow cytometry. Mitochondrial membrane potential was determined by JC-1 staining on a flow cytometer. The activation of Caspase-9, Caspase-3 and cleavage of PARP were measured by Western blot analysis. The protein level of Bcl-2, Bcl-XL and Mcl-1 was monitored by Western blot as well. Chemically synthesized Mcl-1 siRNA was transfected into MGC-803 cells using Lipofectamine 2000 Reagent. The efficacy of gene silencing was confirmed by Western blot analysis, and opoptotic rates before and after transfection was measured by flow cytometry using Annexin V/PI staining. Results UMI-77 was effective in induction of apoptosis in gastric cancer MGC-803 cells, apoptotic rates were increased in a dose-de-pendent manner. Mitochondrial membrane potential was collapsed after UMI-77 treatment. Activation of Caspase-9, Caspase-3 and cleavage of PARP occurred at 24 h (P<0. 05). The expression level of Bcl-2 and Bcl-XL were not altered after exposure to UMI-77 , while Mcl-1 was down-regulated after 12 h ( P<0. 05 ) . Transfection with Mcl-1 siRNA successfully decreased the expression level of Mcl-1 in MGC-803 cells ( P<0. 05 ) and blocked apoptosis induced by UMI-77 ( P<0. 05 ) . Conclusion UMI-77 induces apoptosis through activation of the intrinsic path-way in gastric cancer MGC-803 cells, and knocking down Mcl-1 expression abrogates apoptosis by UMI-77.