Simultaneous inhibition of DNA methyltransferase and histone deacetylase induces p53-independent apoptosis via down-regulation of Mcl-1 in acute myelogenous leukemia cells.

We have recently established the MV4-11 acute myelogenous leukemia (AML) subline, designated as MV4-11 TP53 R248W, which possesses a missense mutation (CGG→TGG; R248W) in the TP53 gene, leading to inactivation of this transcription factor. DNA methyltransferase (DNMT) inhibitor 5-Aza-2'-deoxycytidine (5-AzadC) induced apoptosis in MV4-11, but not in MV4-11 TP53 R248W cells. Another class of anti-epigenetic agent histone deacetylase inhibitor (HDACI) inhibited the proliferation of both MV4-11 and MV4-11 TP53 R248W cells. Notably, when 5-AzadC was combined with HDACI MS-275, apoptosis in MV4-11 TP53 R248W cells was significantly enhanced in parallel with activation of the caspase cascade, up-regulation of p21waf1 and γ-H2AX, and down-regulation of Mcl-1. Interestingly, inhibition of caspase 3 by the pan-caspase inhibitor attenuated the combination of 5-AzadC and MS-275-mediated apoptosis and down-regulation of Mcl-1 in MV4-11 TP53 R248W cells. Moreover, down-regulation of p21waf1 in MV4-11 R248W cells by a small interfering RNA blunted activation of caspase 3 after exposure to the combination of 5-AzadC and MS-275, indicating the role of p21waf1 to activate caspase 3. Taken together, TP53-independent up-regulation of p21waf1 activates caspase 3 and down-regulates Mcl-1 in AML cells. Combination of 5-AzadC and MS-275 may be a promising treatment strategy for individuals with leukemia in which TP53 is inactivated.