SAHA treatment overcomes the anti-apoptotic effects of Bcl-2 and is associated with the formation of mature PML nuclear bodies in human leukemic U937 cells

Bcl-2 protects tumor cells from the apoptotic effects of various antineoplastic agents. Increased expression of Bcl-2 has been associated with poor response to chemotherapy in various malignancies, including leukemia. Therefore, bypassing the resistance conferred by anti-apoptotic factors such as Bcl-2 represents an attractive therapeutic strategy against cancer cells, including leukemic cells. We undertook this study to examine whether SAHA (suberoylanilide hydroxamic acid) overcomes the resistance by Bcl-2 in human leukemic cells, with a specific focus on the involvement of PML-NBs. Experiments were conducted with Bcl-2-overexpressing human leukemic U937 cells. Since we previously demonstrated that overexpression of Bcl-2 attenuates resveratrol-induced apoptosis in human leukemic U937 cells, resveratrol-treated U937 cells were used as a negative control. The present study indicates that SAHA at 1-7 μM, the dose range known to induce apoptosis in various cancer cells, overcomes the anti-apoptotic effects of Bcl-2 in Bcl-2-overexpressing human leukemic U937 cells. Notably, we observed that SAHA-induced formation of mature promyelocytic leukemia (PML) nuclear bodies (NBs) correlates with overcoming the anti-apoptotic effects of Bcl-2 in human leukemic U937 cells. Thus, PML protein and the formation of mature PML-NBs could be considered as therapeutic targets that could help bypass the resistance to apoptosis conferred by Bcl-2. Elucidating exactly how PML regulates Bcl-2 will require further work.